Curable compositions of resin-linear organosiloxane block copolymers

ABSTRACT

Curable compositions of resin-linear organosiloxane block copolymers having improved shelf stability are disclosed. A stabilizer compound is added to the resin-linear organosiloxane block copolymer which increases the temperatures needed to effect final cure of the compositions. In other embodiments, the present disclosure provides curable compositions of resin linear organosiloxane block copolymers having improved physical properties, such as improved toughness.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Appl. Ser. No. 61/566,031, filed Dec. 2, 2011, the entire disclosure of which is incorporated by reference as if fully set forth herein.

BACKGROUND

Light emitting diodes (LEDs) and solar panels use an encapsulant coating to protect photovoltaic cells from environmental factors. Such protective coatings must be optically clear to ensure maximum efficiency of these devices. Furthermore, these protective coatings must also be tough, durable, long lasting, and yet easy to apply. Many of the currently available coatings, however, lack toughness; are not durable; are not long-lasting; and/or are not easy to apply. There is therefore a continuing need to identify protective and/or functional coatings in many areas of emerging technologies.

BRIEF SUMMARY OF THE EMBODIMENTS

The inventors have discovered curable compositions of “resin-linear” organosiloxane block copolymers having improved shelf stability. In particular, the curable composition of resin-linear organosiloxane block copolymers of the embodiments described herein have improved stability resulting from the higher temperatures needed to effect final cure of the compositions. In other embodiments, the disclosure provides curable compositions of resin linear organosiloxane block copolymers having improved physical properties, such as improved “toughness”. In still other embodiments, such “resin-linear” organosiloxane block copolymer, as well as curable compositions and solid compositions derived from these block copolymers offer the significant advantage of being “re-processable” in conjunction with the benefits typically associated with silicones, such as; hydrophobicity, high temperature stability, and moisture/UV resistance. Such “resin-linear” organosiloxane block copolymer, as well as curable compositions and solid compositions derived from these block copolymers, can be processed several times, will cure, and achieve high temperature stability. The melt processability benefits of the “resin-linear” organosiloxane block copolymer, as well as curable compositions and solid compositions derived from these block copolymers, enables the reflow of solid compositions of the organosiloxane block copolymers around device architectures, after an initial coating or solid is formed on the device. This feature is very beneficial to encapsulated various electronic devices. These resin-linear organopolysiloxanes block copolymers also may provide coatings having optical transmission greater than 95%.

Embodiment 1 relates to a curable composition includes:

i) an organosiloxane block copolymer includes:

-   -   40 to 90 mole percent disiloxy units of the formula [R¹         ₂SiO_(2/2)],     -   10 to 60 mole percent trisiloxy units of the formula         [R²SiO_(3/2)],     -   0.5 to 35 mole percent silanol groups [≡SiOH];     -   where:         -   R¹ is independently a C₁ to C₃₀ hydrocarbyl,         -   R² is independently a C₁ to C₂₀ hydrocarbyl;     -   where:         -   the disiloxy units [R₁ ²SiO_(2/2)] are arranged in linear             blocks having an average of from 10 to 400 disiloxy units             [R₁ ²SiO_(2/2)] per linear block,         -   the trisiloxy units [R²SiO_(3/2)] are arranged in non-linear             blocks having a molecular weight of at least 500 g/mol, and             at least 30% of the non-linear blocks are crosslinked with             each other, each linear block is linked to at least one             non-linear block; and     -   the organosiloxane block copolymer has a weight average         molecular weight (M_(w)) of at least 20,000 g/mole; and

ii) a stabilizer.

Embodiment 2 relates to a curable composition of Embodiment 1, further includes a solvent.

Embodiment 3 relates to a curable composition of Embodiment 1 where the stabilizer includes alkaline earth metal salt, a metal chelate, a boron compound, a silicon-containing small-molecule or combinations thereof.

Embodiment 4 relates to a curable composition of Embodiment 2, where the boron compound includes a boric acid derivative.

Embodiment 5 relates to a curable composition of Embodiment 3, where the boric acid derivative includes a boronic acid.

Embodiment 6 relates to a curable composition of Embodiment 4, where the boronic acid includes phenyl boronic acid.

Embodiment 7 relates to a curable composition of Embodiment 1, where the stabilizer includes calcium chloride.

Embodiment 8 relates to a curable composition of Embodiment 3, where the metal chelate includes a metal acetylacetonate complex.

Embodiment 9 relates to a curable composition of Embodiment 8, where the metal is Al, Li, V, Ni, Zr, Mn, Ca, or Mg.

Embodiment 10 relates to a curable composition of Embodiments 1-9, where R² is phenyl.

Embodiment 11 relates to a curable composition of Embodiments 1-10, where R¹ is methyl or phenyl.

Embodiment 12 relates to a curable composition of Embodiments 1-11, where the disiloxy units have the formula [(CH₃)(C₆H₅)SiO_(2/2)].

Embodiment 13 relates to a curable composition of Embodiments 1-12, where the disiloxy units have the formula [(CH₃)₂SiO_(2/2)].

Embodiment 14 relates to a curable composition of any of the above claims, where the stabilizer is a silanol condensation enhancing agent.

Embodiment 15 relates to a solid film composition including a curable composition of Embodiments 1-14.

Embodiment 16 relates to a solid film composition of Embodiment 15, where the film has a trouser tear of at least 0.75 kN/m.

Embodiment 17 relates to a solid film composition of Embodiments 15 or 16, where the solid composition has an optical transmittance of at least 95%.

Embodiment 18 relates to a process for preparing a curable composition including:

-   -   I) reacting         -   a) a linear organosiloxane having the formula:

R¹ _(q)(E)_((3-q))SiO(R¹ ₂SiO_(2/2))_(n)Si(E)_((3-q))R¹ _(q),

-   -   -   -   where each R¹ is independently a C₁ to C₃₀ hydrocarbyl,             -   n is 10 to 400, q is 0, 1, or 2,             -   E is a hydrolyzable group containing at least one carbon                 atom, and

        -   b) an organosiloxane resin comprising at least 60 mol % of             [R²SiO_(3/2)] siloxy             -   units in its formula, where each R² is independently a                 C₁ to C₂₀ hydrocarbyl;

        -   in c) an organic solvent;

        -   to form a resin-linear organosiloxane block copolymer;             -   where the amounts of a) and b) used in step I are                 selected to provide the resin-linear organosiloxane                 block copolymer with 40 to 90 mole % of disiloxy units                 [R₁ ²SiO_(2/2)] and 10 to 60 mole % of trisiloxy units                 [R²SiO_(3/2)], and             -   where at least 95 weight percent of the linear                 organosiloxane added in step I is incorporated into the                 resin-linear organosiloxane block copolymer;

    -   II) reacting the resin-linear organosiloxane block copolymer         from step I) to crosslink the trisiloxy units of the         resin-linear organosiloxane block copolymer sufficiently to         increase the average molecular weight (M_(w)) of the         resin-linear organosiloxane block copolymer by at least 50%;

    -   III) contacting the resin-linear organosiloxane block copolymer         from step II) with a stabilizer; and

    -   IV) optionally, removing the organic solvent.

Embodiment 19 relates to a process of Embodiment 18, where the stabilizer enhances the storage stability of the resin-linear organosiloxane block copolymer relative to the storage stability of a resin-linear organosiloxane block copolymer lacking a stabilizer or that has not been contacted with a stabilizer.

Embodiment 20 relates to a process of Embodiment 18, where the stabilizer in step III) is selected from an alkaline earth metal salt, a metal chelate, a boron compound, a silicon-containing small-molecule or combinations thereof.

Embodiment 21 relates to a process of Embodiment 20, where the alkaline earth metal salt includes calcium chloride.

Embodiment 22 relates to a process of Embodiment 20, where the metal chelate includes a metal acetylacetonate complex.

Embodiment 23 relates to a process of Embodiment 22, where the metal is Al, Li, V, Ni, Zr, Mn, Ca, or Mg.

Embodiment 24 relates to a process of Embodiment 20, where the boron compound includes a boric acid derivative.

Embodiment 25 relates to a process of Embodiment 24, where the boric acid derivative includes a boronic acid.

Embodiment 26 relates to a process of Embodiment 25, where the boronic acid includes phenyl boronic acid.

Embodiment 27 relates to a process of Embodiment 18, wherein the stabilizer is a silanol condensation enhancing agent.

Embodiment 28 relates to a method of increasing the trouser tear strength of a solid curable film composition of a resin linear organopolysiloxane including adding to the composition a stabilizer including an alkaline earth metal salt, a metal chelate, a boron compound, a silicon-containing small molecule or combinations thereof.

Embodiment 29 relates to a method of Embodiment 28, where the trouser tear strength is at least 0.5 kN/m.

Embodiment 30 relates to a method of Embodiment 29, where the boron compound includes a boric acid derivative.

Embodiment 31 relates to a method of Embodiment 30, where the boric acid derivative includes a boronic acid.

Embodiment 32 relates to a method of Embodiment 31, wherein the boronic acid includes phenyl boronic acid.

Embodiment 33 relates to a method of Embodiment 28, where the trouser tear strength of the solid curable film composition is increased by at least 20% with the addition of the stabilizer, relative to solid curable film compositions lacking a stabilizer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The disclosure relates to curable compositions of organosiloxane block copolymers having improved stability. Solid compositions derived from organosiloxane block copolymer compositions may also have improved physical properties such as “toughness”.

The curable compositions of the embodiments described herein comprise:

i) an organosiloxane block copolymer comprising:

-   -   40 to 90 mole percent disiloxy units of the formula [R¹         ₂SiO_(2/2)],     -   10 to 60 mole percent trisiloxy units of the formula         [R²SiO_(3/2)],     -   0.5 to 35 mole percent silanol groups [≡SiOH];     -   wherein:         -   R¹ is independently a C₁ to C₃₀ hydrocarbyl,         -   R² is independently a C₁ to C₂₀ hydrocarbyl,     -   wherein:         -   the disiloxy units [R₁ ²SiO_(2/2)] are arranged in linear             blocks having an average of from 10 to 400 disiloxy units             [R₁ ²SiO_(2/2)] per linear block,         -   the trisiloxy units [R²SiO_(3/2)] are arranged in non-linear             blocks having a molecular weight of at least 500 g/mole, and             at least 30% of the non-linear blocks are crosslinked with             each other, each linear block is linked to at least one             non-linear block, and     -   the organosiloxane block copolymer has an average molecular         weight (M_(w)) of at least 20,000 g/mole; and

ii) a stabilizer.

i) The Organosiloxane Block Copolymer

The organosiloxane block copolymers comprise:

-   -   40 to 90 mole percent disiloxy units of the formula [R¹         ₂SiO_(2/2)],     -   10 to 60 mole percent trisiloxy units of the formula         [R²SiO_(3/2)],     -   0.5 to 35 mole percent silanol groups [≡SiOH];     -   wherein:         -   R¹ is independently a C₁ to C₃₀ hydrocarbyl,         -   R² is independently a C₁ to C₂₀ hydrocarbyl;     -   wherein:         -   the disiloxy units [R¹ ₂SiO_(2/2)] are arranged in linear             blocks having an average of from 10 to 400 disiloxy units             [R¹ ₂SiO_(2/2)] per linear block,         -   the trisiloxy units [R²SiO_(3/2)] are arranged in non-linear             blocks having a molecular weight of at least 500 g/mole, and             at least 30% of the non-linear blocks are crosslinked with             each other, each linear block is linked to at least one             non-linear block; and     -   the organosiloxane block copolymer has a molecular weight of at         least 20,000 g/mole.

The organopolysiloxanes of the embodiments described herein as “resin-linear” organosiloxane block copolymers. Organopolysiloxanes are polymers containing siloxy units independently selected from (R₃SiO_(1/2)), (R₂SiO_(2/2)), (RSiO_(3/2)), or (SiO_(4/2)) siloxy units, where R may be any organic group. These siloxy units are commonly referred to as M, D, T, and Q units respectively. These siloxy units can be combined in various manners to form cyclic, linear, or branched structures. The chemical and physical properties of the resulting polymeric structures vary depending on the number and type of siloxy units in the organopolysiloxane. For example, “linear” organopolysiloxanes typically contain mostly D, or (R₂SiO_(2/2)) siloxy units, which results in polydiorganosiloxanes that are fluids of varying viscosities, depending on the “degree of polymerization” or DP as indicated by the number of D units in the polydiorganosiloxane. “Linear” organopolysiloxanes typically have glass transition temperatures (T_(g)) that are lower than 25° C. “Resin” organopolysiloxanes result when a majority of the siloxy units are selected from T or Q siloxy units. When T siloxy units are predominately used to prepare an organopolysiloxane, the resulting organosiloxane is often referred to as a “resin” or a “silsesquioxane resin”. Increasing the amount of T or Q siloxy units in an organopolysiloxane typically results in polymers having increasing hardness and/or glass like properties. “Resin” organopolysiloxanes thus have higher T_(g) values, for example siloxane resins often have T_(g) values greater than 40° C., e.g., greater than 50° C., greater than 60° C., greater than 70° C., greater than 80° C., greater than 90° C. or greater than 100° C. In some embodiments, T_(g) for siloxane resins is from about 60° C. to about 100° C., e.g., from about 60° C. to about 80° C., from about 50° C. to about 100° C., from about 50° C. to about 80° C. or from about 70° C. to about 100° C.

As used herein “organosiloxane block copolymers” or “resin-linear organosiloxane block copolymers” refer to organopolysiloxanes containing “linear” D siloxy units in combination with “resin” T siloxy units. In some embodiments, the organosiloxane copolymers are “block” copolymers, as opposed to “random” copolymers. As such, the “resin-linear organosiloxane block copolymers” of the disclosed embodiments refer to organopolysiloxanes containing D and T siloxy units, where the D units (i.e., [R¹ ₂SiO_(2/2)] units) are primarily bonded together to form polymeric chains having, in some embodiments, an average of from 10 to 400 D units (e.g., about 10 to about 400 D units; about 10 to about 300 D units; about 10 to about 200 D units; about 10 to about 100 D units; about 50 to about 400 D units; about 100 to about 400 D units; about 150 to about 400 D units; about 200 to about 400 D units; about 300 to about 400 D units; about 50 to about 300 D units; about 100 to about 300 D units; about 150 to about 300 D units; about 200 to about 300 D units; about 100 to about 150 D units, about 115 to about 125 D units, about 90 to about 170 D units or about 110 to about 140 D units), which are referred herein as “linear blocks”.

The T units (i.e., [R²SiO_(3/2)]) are primarily bonded to each other to form branched polymeric chains, which are referred to as “non-linear blocks”. In some embodiments, a significant number of these non-linear blocks may further aggregate to form “nano-domains” when solid forms of the block copolymer are provided. In some embodiments, these nano-domains form a phase separate from a phase formed from linear blocks having D units, such that a resin-rich phase forms. In some embodiments, the disiloxy units [R₁ ²SiO_(2/2)] are arranged in linear blocks having an average of from 10 to 400 disiloxy units [R¹ ₂SiO_(2/2)] per linear block (e.g., about 10 to about 400 D units; about 10 to about 300 D units; about 10 to about 200 D units; about 10 to about 100 D units; about 50 to about 400 D units; about 100 to about 400 D units; about 150 to about 400 D units; about 200 to about 400 D units; about 300 to about 400 D units; about 50 to about 300 D units; about 100 to about 300 D units; about 150 to about 300 D units; about 200 to about 300 D units; about 100 to about 150 D units, about 115 to about 125 D units, about 90 to about 170 D units or about 110 to about 140 D units), and the trisiloxy units [R²SiO_(3/2)] are arranged in non-linear blocks having a molecular weight of at least 500 g/mole and at least 30% of the non-linear blocks are crosslinked with each other.

In some embodiments, the non-linear blocks have a number average molecular weight of at least 500 g/mole, e.g., at least 1000 g/mole, at least 2000 g/mole, at least 3000 g/mole or at least 4000 g/mole; or have a molecular weight of from about 500 g/mole to about 4000 g/mole, from about 500 g/mole to about 3000 g/mole, from about 500 g/mole to about 2000 g/mole, from about 500 g/mole to about 1000 g/mole, from about 1000 g/mole to 2000 g/mole, from about 1000 g/mole to about 1500 g/mole, from about 1000 g/mole to about 1200 g/mole, from about 1000 g/mole to 3000 g/mole, from about 1000 g/mole to about 2500 g/mole, from about 1000 g/mole to about 4000 g/mole, from about 2000 g/mole to about 3000 g/mole or from about 2000 g/mole to about 4000 g/mole.

In some embodiments, at least 30% of the non-linear blocks are crosslinked with each other, e.g., at least 40% of the non-linear blocks are crosslinked with each other; at least 50% of the non-linear blocks are crosslinked with each other; at least 60% of the non-linear blocks are crosslinked with each other; at least 70% of the non-linear blocks are crosslinked with each other; or at least 80% of the non-linear blocks are crosslinked with each other. In other embodiments, from about 30% to about 80% of the non-linear blocks are crosslinked with each other; from about 30% to about 70% of the non-linear blocks are crosslinked with each other; from about 30% to about 60% of the non-linear blocks are crosslinked with each other; from about 30% to about 50% of the non-linear blocks are crosslinked with each other; from about 30% to about 40% of the non-linear blocks are crosslinked with each other; from about 40% to about 80% of the non-linear blocks are crosslinked with each other; from about 40% to about 70% of the non-linear blocks are crosslinked with each other; from about 40% to about 60% of the non-linear blocks are crosslinked with each other; from about 40% to about 50% of the non-linear blocks are crosslinked with each other; from about 50% to about 80% of the non-linear blocks are crosslinked with each other; from about 50% to about 70% of the non-linear blocks are crosslinked with each other; from about 55% to about 70% of the non-linear blocks are crosslinked with each other, from about 50% to about 60% of the non-linear blocks are crosslinked with each other; from about 60% to about 80% of the non-linear blocks are crosslinked with each other; or from about 60% to about 70% of the non-linear blocks are crosslinked with each other.

The organosiloxane block copolymers (e.g., those comprising 40 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)] and 10 to 60 mole percent trisiloxy units of the formula [R²SiO_(3/2)]) may be represented by the formula [R₁ ²SiO_(2/2)]_(a)[R²SiO_(3/2)]_(b) where the subscripts a and b represent the mole fractions of the siloxy units in the copolymer,

a may vary from 0.4 to 0.9,

-   -   alternatively from 0.5 to 0.9,         -   alternatively from 0.6 to 0.9,

b may vary from 0.1 to 0.6,

-   -   alternatively from 0.1 to 0.5,         -   alternatively from 0.1 to 0.4,

R¹ is independently a C₁ to C₃₀ hydrocarbyl,

R² is independently a C₁ to C₁₀ hydrocarbyl.

In some embodiments, the organosiloxane block copolymers of the embodiments described herein comprise 40 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)], e.g., 50 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 60 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 65 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 70 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; or 80 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 40 to 80 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 40 to 70 mole percent disiloxy units of the formula [R₁ ²SiO_(2/2)]; 40 to 60 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 40 to 50 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 50 to 80 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 50 to 70 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 50 to 60 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 60 to 80 mole percent disiloxy units of the formula [R₁ ²SiO_(2/2)]; 60 to 70 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; or 70 to 80 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)].

In some embodiments, the organosiloxane block copolymers of the embodiments described herein comprise 10 to 60 mole percent trisiloxy units of the formula [R²SiO_(3/2)], e.g., 10 to 20 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 10 to 30 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 10 to 35 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 10 to 40 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 10 to 50 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 20 to 30 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 20 to 35 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 20 to 40 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 20 to 50 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 20 to 60 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 30 to 40 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 30 to 50 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 30 to 60 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 40 to 50 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; or 40 to 60 mole percent trisiloxy units of the formula [R²SiO_(3/2)] It should be understood that the organosiloxane block copolymers of the embodiments described herein may contain additional siloxy units, such as M siloxy units, Q siloxy units, other unique D or T siloxy units (for example having organic groups other than R¹ or R²), provided that the organosiloxane block copolymer contains the mole fractions of the disiloxy and trisiloxy units as described above. In other words, the sum of the mole fractions as designated by subscripts a and b, do not necessarily have to sum to one. The sum of a+b may be less than one to account for minor amounts of other siloxy units that may be present in the organosiloxane block copolymer. Alternatively, the sum of a+b is greater than 0.6, alternatively greater than 0.7, alternatively greater than 0.8, or alternatively greater than 0.9. In some embodiments, the sum of a+b is from about 0.6 to about 0.9, e.g., from about 0.6 to about 0.8, from about 0.6 to about 0.7, from about 0.7 to about 0.9, from about 0.7 to about 0.8, or from about 0.8 to about 0.9.

In one embodiment, the organosiloxane block copolymer consists essentially of the disiloxy units of the formula [R¹ ₂SiO_(2/2)] and trisiloxy units of the formula [R²SiO_(3/2)], while also containing 0.5 to 25 mole percent silanol groups [≡SiOH] (e.g., 0.5 to 5 mole percent, 0.5 to 10 mole percent, 0.5 to 15 mole percent, 0.5 to 20 mole percent, 5 to 10 mole percent, 5 to 15 mole percent, 5 to 20 mole percent, 5 to 25 mole percent, 10 to 15 mole percent 10 to 20 mole percent, 10 to 25 mole percent, 15 to 20 mole percent, 15 to 25 mole percent, or to 25 mole percent), where R¹ and R² are as defined above. Thus, in this embodiment, the sum of a+b (when using mole fractions to represent the amount of disiloxy and trisiloxy units in the copolymer) is greater than 0.95, alternatively greater than 0.98.

In some embodiments, the resin-linear organosiloxane block copolymers also contain silanol groups (SiOH). The amount of silanol groups present on the organosiloxane block copolymer may vary from 0.5 to 35 mole percent silanol groups [≡SiOH],

alternatively from 2 to 32 mole percent silanol groups [≡SiOH],

alternatively from 8 to 22 mole percent silanol groups [≡SiOH].

The silanol groups may be present on any siloxy units within the organosiloxane block copolymer. The amount described above represent the total amount of silanol groups found in the organosiloxane block copolymer. In some embodiments, the majority (e.g., greater than 75%, greater than 80%, greater than 90%; from about 75% to about 90%, from about 80% to about 90%, or from about 75% to about 85%) of the silanol groups will reside on the trisiloxy units, i.e., the resin component of the block copolymer. Although not wishing to be bound by any theory, the silanol groups present on the resin component of the organosiloxane block copolymer allows for the block copolymer to further react or cure at elevated temperatures.

R¹ in the above disiloxy unit formula is independently a C₁ to C₃₀ hydrocarbyl. The hydrocarbon group may independently be an alkyl, aryl, or alkylaryl group. As used herein, hydrocarbyl also includes halogen substituted hydrocarbyls, where the halogen may be chlorine, fluorine, bromine or combinations thereof. R¹ may be a C₁ to C₃₀ alkyl group, alternatively R¹ may be a C₁ to C₁₈ alkyl group. Alternatively R¹ may be a C₁ to C₆ alkyl group such as methyl, ethyl, propyl, butyl, pentyl, or hexyl. Alternatively R¹ may be methyl. R¹ may be an aryl group, such as phenyl, naphthyl, or an anthryl group. Alternatively, R¹ may be any combination of the aforementioned alkyl or aryl groups. Alternatively, R¹ is phenyl, methyl, or a combination of both.

Each R² in the above trisiloxy unit formula is independently a C₁ to C₂₀ hydrocarbyl. As used herein, hydrocarbyl also includes halogen substituted hydrocarbyls, where the halogen may be chlorine, fluorine, bromine or combinations thereof. R² may be an aryl group, such as phenyl, naphthyl, anthryl group. Alternatively, R² may be an alkyl group, such as methyl, ethyl, propyl, or butyl. Alternatively, R² may be any combination of the aforementioned alkyl or aryl groups. Alternatively, R² is phenyl or methyl.

The formula [R₁ ²SiO_(2/2)]_(a)[R²SiO_(3/2)]_(b), and related formulae using mole fractions, as used herein to describe the organosiloxane block copolymers, does not indicate structural ordering of the disiloxy [R¹ ₂SiO_(2/2)] and trisiloxy [R²SiO_(3/2)] units in the copolymer. Rather, this formula is meant to provide a convenient notation to describe the relative amounts of the two units in the copolymer, as per the mole fractions described above via the subscripts a and b. The mole fractions of the various siloxy units in the present organosiloxane block copolymers, as well as the silanol content, may be readily determined by ²⁹Si NMR techniques, as detailed in the Examples.

The organosiloxane block copolymers of the embodiments described herein have a weight average molecular weight (M_(w)) of at least 20,000 g/mole, alternatively a weight average molecular weight of at least 40,000 g/mole, alternatively a weight average molecular weight of at least 50,000 g/mole, alternatively a weight average molecular weight of at least 60,000 g/mole, alternatively a weight average molecular weight of at least 70,000 g/mole, or alternatively a weight average molecular weight of at least 80,000 g/mole. In some embodiments, the organosiloxane block copolymers of the embodiments described herein have a weight average molecular weight (M_(w)) of from about 20,000 g/mole to about 250,000 g/mole or from about 100,000 g/mole to about 250,000 g/mole, alternatively a weight average molecular weight of from about 40,000 g/mole to about 100,000 g/mole, alternatively a weight average molecular weight of from about 50,000 g/mole to about 100,000 g/mole, alternatively a weight average molecular weight of from about 50,000 g/mole to about 80,000 g/mole, alternatively a weight average molecular weight of from about 50,000 g/mole to about 70,000 g/mole, alternatively a weight average molecular weight of from about 50,000 g/mole to about 60,000 g/mole. The average molecular weight may be readily determined using Gel Permeation Chromatography (GPC) techniques, such as those described in the Examples. In some embodiments, the organosiloxane block copolymers of the embodiments described herein have a number average molecular weight (M_(n)) of from about 15,000 to about 50,000 g/mole; from about 15,000 to about 30,000 g/mole; from about 20,000 to about 30,000 g/mole; or from about 20,000 to about 25,000 g/mole.

In some embodiments, the structural ordering of the disiloxy and trisiloxy units may be further described as follows: the disiloxy units [R¹ ₂SiO_(2/2)] are arranged in linear blocks having an average of from 10 to 400 disiloxy units [R¹ ₂SiO_(2/2)] per linear block, and the trisiloxy units [R²SiO_(3/2)] are arranged in non-linear blocks having a molecular weight of at least 500 g/mole. Each linear block is linked to at least one non-linear block in the block copolymer. Furthermore, at least 30% of the non-linear blocks are crosslinked with each other,

alternatively at least at 40% of the non-linear blocks are crosslinked with each other,

alternatively at least at 50% of the non-linear blocks are crosslinked with each other.

In other embodiments, from about 30% to about 80% of the non-linear blocks are crosslinked with each other; from about 30% to about 70% of the non-linear blocks are crosslinked with each other; from about 30% to about 60% of the non-linear blocks are crosslinked with each other; from about 30% to about 50% of the non-linear blocks are crosslinked with each other; from about 30% to about 40% of the non-linear blocks are crosslinked with each other; from about 40% to about 80% of the non-linear blocks are crosslinked with each other; from about 40% to about 70% of the non-linear blocks are crosslinked with each other; from about 40% to about 60% of the non-linear blocks are crosslinked with each other; from about 40% to about 50% of the non-linear blocks are crosslinked with each other; from about 50% to about 80% of the non-linear blocks are crosslinked with each other; from about 50% to about 70% of the non-linear blocks are crosslinked with each other; from about 50% to about 60% of the non-linear blocks are crosslinked with each other; from about 60% to about 80% of the non-linear blocks are crosslinked with each other; or from about 60% to about 70% of the non-linear blocks are crosslinked with each other.

The crosslinking of the non-linear blocks may be accomplished via a variety of chemical mechanisms and/or moieties. For example, crosslinking of non-linear blocks within the block copolymer may result from the condensation of residual silanol groups present in the non-linear blocks of the copolymer. Crosslinking of the non-linear blocks within the block copolymer may also occur between “free resin” components and the non-linear blocks. “Free resin” components may be present in the block copolymer compositions as a result of using an excess amount of an organosiloxane resin during the preparation of the block copolymer. The free resin component may crosslink with the non-linear blocks by condensation of the residual silanol groups present on the non-blocks and on the free resin. The free resin may provide crosslinking by reacting with lower molecular weight compounds added as crosslinkers, as described below. The free resin, when present, may be present in an amount of from about 10% to about 20% by weight of the organosiloxane block copolymers of the embodiments described herein, e.g., from about 15% to about 20% by weight organosiloxane block copolymers of the embodiments described herein.

Alternatively, certain compounds may be added during the preparation of the block copolymer to specifically crosslink the non-resin blocks. These crosslinking compounds may include an organosilane having the formula R⁵ _(q)SiX_(4-q), which is added during the formation of the block copolymer (step II as discussed below), where R⁵ is a C₁ to C₈ hydrocarbyl or a C₁ to C₈ halogen-substituted hydrocarbyl; X is a hydrolyzable group; and q is 0, 1, or 2. R⁵ is a C₁ to C₈ hydrocarbyl or a C₁ to C₈ halogen-substituted hydrocarbyl, or alternatively R⁵ is a C₁ to C₈ alkyl group, or alternatively a phenyl group, or alternatively R⁵ is methyl, ethyl, or a combination of methyl and ethyl. X is any hydrolyzable group, alternatively X may be an oximo, acetoxy, halogen atom, hydroxyl (OH), or an alkoxy group.

In one embodiment, the organosilane having the formula R⁵ _(q)SiX_(4-q) is an alkyltriacetoxysilane, such as methyltriacetoxysilane, ethyltriacetoxysilane, or a combination of both. Commercially available representative alkyltriacetoxysilanes include ETS-900 (Dow Corning Corp., Midland, Mich.).

Other suitable, non-limiting organosilanes useful as crosslinkers include; methyl-tris(methylethylketoxime)silane (MTO), methyl triacetoxysilane, ethyl triacetoxysilane, tetraacetoxysilane, tetraoximesilane, dimethyl diacetoxysilane, dimethyl dioximesilane, methyl tris(methylmethylketoxime)silane.

The crosslinks within the block copolymer will primarily be siloxane bonds, ≡Si—O—Si≡, resulting from the condensation of silanol groups, as discussed above.

The amount of crosslinking in the block copolymer may be estimated by determining the average molecular weight of the block copolymer, such as with GPC techniques. Typically, crosslinking the block copolymer increases its average molecular weight. Thus, an estimation of the extent of crosslinking may be made, given the average molecular weight of the block copolymer, the selection of the linear siloxy component (that is the chain length as indicated by its degree of polymerization), and the molecular weight of the non-linear block (which is primarily controlled by the selection of the selection of the organosiloxane resin used to prepare the block copolymer).

The curable compositions of the embodiments described herein may further comprise an organic solvent. The organic solvent typically is an aromatic solvent, such as benzene, toluene, or xylene.

The curable compositions of the embodiments described herein may further contain an organosiloxane resin (e.g., free resin that is not part of the block copolymer). The organosiloxane resin present in these compositions typically will be the organosiloxane resin used to prepare the organosiloxane block copolymer. Thus, the organosiloxane resin may comprise at least 60 mol % of [R²SiO_(3/2)] siloxy units in its formula (e.g., at least 70 mol % of [R²SiO_(3/2)] siloxy units, at least 80 mole % of [R²SiO_(3/2)] siloxy units, at least 90 mole % of [R²SiO_(3/2)] siloxy units, or 100 mole % of [R²SiO_(3/2)] siloxy units; or 60-100 mole % [R²SiO_(3/2)] siloxy units, 60-90 mole % [R²SiO_(3/2)] siloxy units or 70-80 mole % [R²SiO_(3/2)] siloxy units), where each R² is independently a C₁ to C₂₀ hydrocarbyl. Alternatively, the organosiloxane resin is a silsesquioxane resin, or alternatively a phenyl silsesquioxane resin.

The organosiloxane block copolymer of the embodiments described herein may be prepared by the methods known in the art, including the methods disclosed in Published PCT Application Nos. WO2012/040302 and WO2012/040305, which are incorporated herein by reference in their entirety.

ii) The Stabilizer

A stabilizer is added to the resin-linear organosiloxane block copolymers, as described above, to improve shelf stability and/or other physical properties of solid compositions containing the organosiloxane block copolymers. The stabilizer may be selected from an alkaline earth metal salt, a metal chelate, a boron compound, a silicon-containing small molecule or combinations thereof.

Although not wishing to be bound by any theory, the stabilizer component may behave as a condensation catalyst. For example, treatment with a salt such as calcium chloride or catalysts like metal chelates (e.g., magnesium acetylacetonate or Al(acac)₃) during the synthesis (e.g., at the end of synthesis) of the resin-linear organosiloxane block copolymers of the embodiments described herein, greatly increases the stability of the product. This is surprising and unexpected, since catalysts would be expected to reduce shelf stability of the silanol functional copolymers. However, while not being bound by theory, it is believed that, in some cases, the stabilizers may be preferentially soluble in the phase separated resin-rich phase and enhance condensation of the silanol groups present in this phase. Since this phase (i.e., the resin-rich phase) mainly contains residual “free resin”, condensation of this phase can subsequently increase the cure temperature of the matrix containing the resin-linear block copolymers. For example, in the absence of the stabilizers of the embodiments described herein, a typical resin-linear material with elastomeric behavior (e.g., based on 20 mole % Phenyl-silsesquioxane resin and 184 dp polydimethylsiloxane, also known as “PDMS”), will have a flow onset around 80° C. followed by further condensation cure around 120° C. from residual silanol groups residing on the resin blocks, resulting in a material with tensile strength from 2-5 MPa and elongation at break from 200-600%. The same resin-linear material comprising a stabilizer will have its cure temperature significantly extended from 120 to 180° C.

In sum, in some embodiments, the stabilizer, in its broadest sense, may be considered a silanol condensation enhancing agent (i.e., a condensation catalyst). In some embodiments, the silanol condensation enhancing agent may substantially reside in the phase separated resin rich phase and enhances silanol condensation in that phase, thereby reducing the mole % of reactive silanol groups in that phase. In some embodiments, the silanol condensation enhancing agent will be more likely to reside in the phase separated resin rich phase when the silanol condensation enhancing agent is more compatible (e.g., soluble) with that phase than, e.g., in the organosiloxane block copolymer-rich phase, and less likely to reside in the phase separated resin rich phase when the silanol condensation enhancing agent is less compatible with phase separated resin rich phase. In some embodiments, the mole % of reactive silanol groups in the phase separated resin rich phase is reduced by about 25%, e.g., by about 35%, by about 45%, by about 55%, by about 65%, by about 75%, by about 85%, or by about 95% relative to the mole % reactive silanol groups that would be present in the phase separated resin rich phase if the stabilizer were not present. In some embodiments, the mole % of reactive silanol groups in the phase separated resin rich phase is reduced from about 25% to about 95%, e.g., from about 25% to about 55%, from about 25% to about 75%, from about 35% to about 75%, from about 55% to about 95% or from about 55% to about 85% relative to the mol % reactive silanol groups that would be present in the phase separated resin rich phase if the stabilizer were not present.

The stabilizer ii) is combined with the organosiloxane block copolymer i) as described above. The method by which they are combined may vary and is not limiting, but typically the stabilizer is added to the resin-linear organosiloxane block copolymer or a composition containing the block copolymer. Alternatively, curable compositions containing the two components may be prepared by the methods described further below.

In one embodiment, the stabilizer comprises an alkaline earth metal salt. As used herein the term “alkaline earth metal salt” includes, but is not limited to, salts of magnesium and calcium. Non-limiting examples of salts of magnesium include magnesium chloride. Non-limiting examples of salts of calcium include calcium chloride. For example, calcium chloride enhances the stability of organic solutions of resin-linear organosiloxane block copolymers. The enhanced stability associated with alkaline earth metal salt, as well as or the other stabilizers disclosed herein, may be assessed by monitoring the time needed to gel a solution of the resin-linear organosiloxane block copolymer at slightly elevated temperatures (such as 40° C., see examples for further details). The amount of the alkaline earth metal salt combined with the resin-linear organosiloxane block copolymer may vary, but typically, 1 to 100, alternatively 5 to 50, or alternatively 10 to 25 parts by weight of the alkaline earth metal salt is added for every 100 parts by weight of the resin-linear organosiloxane block copolymer of the embodiments described herein.

In another embodiment, the stabilizer comprises a metal chelate such as a metal acetylacetonate (acac). Representative metal acetylacetonate complexes suitable as a stabilizer include, but are not limited to, aluminum, lithium, vanadium, nickel, zirconium, manganese, calcium, and magnesium acetylacetonate complexes. The amount of the metal chelate combined with the resin-linear organosiloxane block copolymer may vary, but typically the amounts are selected based on providing a certain metal concentration in the compositions containing the resin-linear organosiloxane block copolymer. The metal concentrations in the compositions may be expressed in parts per million (ppm). Typically the metal concentrations in the compositions containing the resin-linear organosiloxane block copolymer varies from 1 to 1000 ppm, alternatively 10 to 500 ppm, 100 to 400 ppm, 50 to 300 ppm, 50 to 250 ppm, 50 to 100 ppm, 100 to 250 ppm, 150 to 250 ppm, 150 to 200 ppm or alternatively from 200 to 300 ppm.

In other embodiments, the stabilizer comprises a boron compound. In some embodiments, the boron compound comprises a derivative of boric acid (i.e., derivatives of B(OH)₃), compounds that contain B—OH units, or any boron compounds known to affect silanol condensation reactions (e.g., boron nitride and boron oxide). In one embodiment, the stabilizer is a boric acid derivative. Boric acid derivatives include, but are not limited to boronic acids including isobuteneboronic acid, (2-methylpropyl) boronic acid, phenyl boronic acid, (C₆H₅)B(OH)₂, and any other boronic acid comprising an aromatic group, including 4-formylphenyl boronic acid, 2-hydroxy-3-methylphenyl boronic acid, (2,6-dimethoxy-4-methylphenyl)boronic acid, (2-fluoro-5-methoxycarbonylphenyl)boronic acid, (3-chloro-2-methylphenyl)boronic acid, (3-ethoxy-5-fluorophenyl)boronic acid, (3-fluoro-5-ethoxycarbonylphenyl)boronic acid, (3-fluoro-5-isopropoxyphenyl)boronic acid, (3-fluoro-5-methoxycarbonylphenyl)boronic acid, (3-fluoro-5-methylphenyl)boronic acid, (3-methoxy-5-(trifluoromethyl)phenyl)boronic acid, (3-t-butyl-5-methylphenyl)boronic acid, (4-bromo-2,5-dimethylphenyl)boronic acid, (4-fluoro-3-methoxyphenyl)boronic acid, (4-methoxy-3-trifluoromethylphenyl)boronic acid, and the like. See, e.g., http://www.sigmaaldrich.com/chemistry/special-offers/boronic-acid.html?cm_sp=Insite-_-ChemSynth-_-BoronicAcidPromo for additional other boronic acid comprising an aromatic group.

The amount of boric acid derivative, compounds that contain B—OH units, or the amount of boron compound known to affect silanol condensation reactions may vary, but typically the amount selected is based on the mole ratio of the OH groups of the boric acid derivative, compounds that contain B—OH units, or the amount of boron compound known to affect silanol condensation reactions to the Si—OZ content (amount of Si—OH or Si-alkoxy) on the resin components of the resin-linear organosiloxane block copolymer compositions. Typically the mole ratio of the OH groups of boric acid derivative, compounds that contain B—OH units, or the amount of boron compound known to affect silanol condensation reactions to the Si—OZ content of the resin-linear organosiloxane block copolymers is 0.1/50, alternatively 0.5/20, or alternatively 1/10. In some embodiments, the mole ratio of the OH groups of boric acid derivative, compounds that contain B—OH units, or the amount of boron compound known to affect silanol condensation reactions to the Si—OZ content of the resin-linear organosiloxane block copolymers is 0.1/50 to 1/10, e.g., from 0.1/50 to 0.5/20, from 0.5/20 to 1/10 or from 0.5/20 to 5/20. In some embodiments, the boric acid derivative comprises phenyl boronic acid.

In some embodiments, the stabilizer comprises a silicon-containing small molecule. As used herein, the term “silicon-containing small molecule” includes, but is not limited to compounds of the formula:

wherein each R₁ is the same or different and may be a C₁-C₃₀ hydrocarbyl group, as the group is defined previously. Non-limiting examples of such silicon-containing small molecules include Ph₂MeSiOH and Ph₃SiOH.

The term “silicon-containing small molecule” also includes silanes of the formula:

wherein each R₁ is the same or different and may be a C₁-C₃₀ hydrocarbyl group, as the group is defined previously; and R is R₁ or hydrogen. Non-limiting examples of such silanes include, but are not limited to triphenyl silane (Ph₃SiH) and tetraphenyl silane (Ph₄Si).

As used herein, the term “small molecule” refers to molecules not exceeding 1000 g/mole.

In some embodiments, the silicon-containing small molecule stabilizer is used in combination with one or more other stabilizers. For example, the silicon-containing small molecule could be used in combination with an alkaline earth metal salt, a metal chelate or a boron compound. In some embodiments, the silicon-containing small molecule is used in combination with a metal chelate (e.g., Al(acac)₃). In some embodiments, the silicon-containing small molecule stabilizer is added during the preparation/synthesis of the block copolymers of the embodiments described herein. In other embodiments, the silicon-containing small molecule stabilizer is added after the block copolymers of the embodiments described herein have been prepared/synthesized.

In some embodiments, the amount of the silicon-containing small molecule that me be used is less than 15 wt %, e.g., less than 10 wt %, less than 5 wt %, less than 2 wt %, less than 1 wt % or less than 0.5 wt %. In some embodiments, the amount of the silicon-containing small molecule that me be used is from about 0.1 wt % to about 10 wt %, e.g., from about 0.1 wt % to about 0.5 wt %, from about 0.25 wt % to about 1 wt %, from about 1 wt % to about 5 wt %, from about 2 wt % to about 10 wt % or from about 2 wt % to about 5 wt %.

The present disclosure further provides curable compositions comprising:

a) the organosiloxane block copolymers as described above in combination with the stabilizer as described above, and

b) an organic solvent.

In some embodiments, the organic solvent is an aromatic solvent, such as benzene, toluene, or xylene.

In one embodiment, the curable compositions may further contain an organosiloxane resin (e.g., free resin that is not part of the block copolymer). The organosiloxane resin present in these compositions is, in some embodiments, the same organosiloxane resin used to prepare the organosiloxane block copolymer. Thus, the organosiloxane resin may comprise at least 60 mole % of [R²SiO_(3/2)] siloxy units in its formula (e.g., at least 70 mole % of [R²SiO_(3/2)] siloxy units or at least 80 mole % of [R₂SiO_(3/2)] siloxy units; or 60-70 mole % [R²SiO_(3/2)] siloxy units, 60-80 mole % [R²SiO_(3/2)] siloxy units or 70-80 mole % [R²SiO_(3/2)] siloxy units), where each R² is independently a C₁ to C₂₀ hydrocarbyl. Alternatively, the organosiloxane resin is a silsesquioxane resin, or alternatively a phenyl silsesquioxane resin.

The amount of the organosiloxane block copolymers, organic solvent, and optional organosiloxane resin in the present curable composition may vary. The curable composition of the present disclosure may contain:

-   -   40 to 80 weight % of the organosiloxane block copolymer as         described above (e.g., 40 to 70 weight %, 40 to 60 weight %, 40         to 50 weight %);     -   10 to 80 weight % of the organic solvent (e.g., 10 to 70 weight         %, 10 to 60 weight %, 10 to 50 weight %, 10 to 40 weight %, 10         to 30 weight %, 10 to 20 weight %, 20 to 80 weight %, 30 to 80         weight %, 40 to 80 weight %, 50 to 80 weight %, 60 to 80 weight         %, or 70 to 80 weight; and     -   5 to 40 weight % of the organosiloxane resin (e.g., 5 to 30         weight %, 5 to 20 weight %, 5 to 10 weight %, 10 to 40 weight %,         10 to 30 weight %, 10 to 20 weight %, 20 to 40 weight % or 30 to         40 weight %).         Such that the sum of the weight % of these components does not         exceed 100%. In one embodiment, the curable compositions consist         essentially of the organosiloxane block copolymer as described         above, the organic solvent, and the organosiloxane resin. In         this embodiment, the weight % of these components sum to 100%,         or nearly 100%.

In yet another embodiment, the curable compositions contain a cure catalyst. The cure catalyst may be selected from any catalyst known in the art to affect condensation cure of organosiloxanes, such as various tin or titanium catalysts. Condensation catalyst can be any condensation catalyst typically used to promote condensation of silicon bonded hydroxy (=silanol) groups to form Si—O—Si linkages. Examples include, but are not limited to, amines, complexes of lead, tin, titanium, zinc, and iron.

The organosiloxane block copolymers and curable compositions containing the organosiloxane block copolymer may be prepared by the methods as described further below. Representative examples of their preparation are also detailed in the Examples section below.

Solid compositions containing the resin-linear organosiloxane block copolymers may be prepared by removing the solvent from the curable organosiloxane block copolymer compositions as described above. The solvent may be removed by any known processing techniques. In one embodiment, a film of the curable compositions containing the organosiloxane block copolymers is formed, and the solvent is allowed to evaporate from the film. Subjecting the films to elevated temperatures, and/or reduced pressures, will accelerate solvent removal and subsequent formation of the solid curable composition. Alternatively, the curable compositions may be passed through an extruder to remove solvent and provide the solid composition in the form of a ribbon or pellets. Coating operations against a release film could also be used as in slot die coating, knife over roll, rod, or gravure coating. Also, roll-to-roll coating operations could be used to prepare a solid film. In coating operations, a conveyer oven or other means of heating and evacuating the solution can be used to drive off the solvent and obtain the final solid film.

Although not wishing to be bound by any theory, it is believed that the structural ordering of the disiloxy and trisiloxy units in the organosiloxane block copolymer as described above may provide the copolymer with certain unique physical property characteristics when solid compositions of the block copolymer are formed. For example, the structural ordering of the disiloxy and trisiloxy units in the copolymer may provide solid coatings that allow for a high optical transmittance of visible light (e.g., at wavelengths above 350300 nm). The structural ordering may also allow the organosiloxane block copolymer to flow and cure upon heating, yet remain stable at room temperature. They may also be processed using lamination techniques. These properties are useful to provide coatings for various electronic articles to improve weather resistance and durability, while providing low cost and easy procedures that are energy efficient.

The present disclosure further relates to solid forms of the aforementioned organosiloxane block copolymers and solid compositions derived from the curable compositions described above comprising the organosiloxane block copolymers. Thus, the present disclosure provides organosiloxane block copolymers comprising:

-   -   40 to 90 mole percent disiloxy units of the formula [R¹         ₂SiO_(2/2)],     -   10 to 60 mole percent trisiloxy units of the formula         [R²SiO_(3/2)],     -   0.5 to 25 mole percent silanol groups [≡SiOH];     -   wherein:         -   R¹ is independently a C₁ to C₃₀ hydrocarbyl,         -   R² is independently a C₁ to C₂₀hydrocarbyl;     -   wherein:         -   the disiloxy units [R¹ ₂SiO_(2/2)] are arranged in linear             blocks having an average of from 10 to 400 disiloxy units             [R¹ ₂SiO_(2/2)] per linear block,         -   the trisiloxy units [R²SiO_(3/2)] are arranged in non-linear             blocks having a molecular weight of at least 500 g/mole, at             least 30% of the non-linear blocks are crosslinked with each             other and are predominately aggregated together in             nano-domains, each linear block is linked to at least one             non-linear block; and     -   the organosiloxane block copolymer has a weight average         molecular weight of at least 20,000 g/mole, and is a solid at         25° C.

In some embodiments, the organosiloxane block copolymers contained in the solid forms and solid compositions comprise 40 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)], e.g., 50 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 60 to 90 mole percent disiloxy units of the formula [R₁ ²SiO_(2/2)]; 65 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 70 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; or 80 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 40 to 80 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 40 to 70 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 40 to 60 mole percent disiloxy units of the formula [R₁ ²SiO_(2/2)]; 40 to 50 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 50 to 80 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 50 to 70 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 50 to 60 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 60 to 80 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 60 to 70 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; or 70 to 80 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)].

In some embodiments, the organosiloxane block copolymers contained in the solid forms and solid compositions comprise 10 to 60 mole percent trisiloxy units of the formula [R²SiO_(3/2)], e.g., 10 to 20 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 10 to 30 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 10 to 35 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 10 to 40 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 10 to 50 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 20 to 30 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 20 to 35 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 20 to 40 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 20 to 50 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 20 to 60 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 30 to 40 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 30 to 50 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 30 to 60 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 40 to 50 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; or 40 to 60 mole percent trisiloxy units of the formula [R²SiO_(3/2)].

In some embodiments, the organosiloxane block copolymers contained in the solid forms and solid compositions comprise 0.5 to 25 mole percent silanol groups [≡SiOH] (e.g., 0.5 to 5 mole percent, 0.5 to 10 mole percent, 0.5 to 15 mole percent, 0.5 to 20 mole percent, 5 to 10 mole percent, 5 to 15 mole percent, 5 to 20 mole percent, 5 to 25 mole percent, 10 to 15 mole percent 10 to 20 mole percent, 10 to 25 mole percent, 15 to 20 mole percent, 15 to 25 mole percent, or 20 to 25 mole percent).

In some embodiments, the disiloxy units [R¹ ₂SiO_(2/2)] in the organosiloxane block copolymers contained in the solid forms and solid compositions are arranged in linear blocks having an average of 10 to 400 disiloxy units, e.g., about 10 to about 400 disiloxy units; about 10 to about 300 disiloxy units; about 10 to about 200 disiloxy units; about 10 to about 100 disiloxy units; about 50 to about 400 disiloxy units; about 100 to about 400 disiloxy units; about 150 to about 400 disiloxy units; about 200 to about 400 disiloxy units; about 300 to about 400 disiloxy units; about 50 to about 300 disiloxy units; about 100 to about 300 disiloxy units; about 150 to about 300 disiloxy units; about 200 to about 300 disiloxy units; about 100 to about 150 disiloxy units, about 115 to about 125 disiloxy units, about 90 to about 170 disiloxy units or about 110 to about 140 disiloxy units).

In some embodiments, the non-linear blocks in the organosiloxane block copolymers contained in the solid forms and solid compositions have a number average molecular weight of at least 500 g/mole, e.g., at least 1000 g/mole, at least 2000 g/mole, at least 3000 g/mole or at least 4000 g/mole; or have a molecular weight of from about 500 g/mole to about 4000 g/mole, from about 500 g/mole to about 3000 g/mole, from about 500 g/mole to about 2000 g/mole, from about 500 g/mole to about 1000 g/mole, from about 1000 g/mole to 2000 g/mole, from about 1000 g/mole to about 1500 g/mole, from about 1000 g/mole to about 1200 g/mole, from about 1000 g/mole to 3000 g/mole, from about 1000 g/mole to about 2500 g/mole, from about 1000 g/mole to about 4000 g/mole, from about 2000 g/mole to about 3000 g/mole or from about 2000 g/mole to about 4000 g/mole.

In some embodiments, at least 30% of the non-linear blocks in the organosiloxane block copolymers contained in the solid forms and solid compositions are crosslinked with each other, e.g., at least 40% of the non-linear blocks are crosslinked with each other; at least 50% of the non-linear blocks are crosslinked with each other; at least 60% of the non-linear blocks are crosslinked with each other; at least 70% of the non-linear blocks are crosslinked with each other; or at least 80% of the non-linear blocks are crosslinked with each other. In other embodiments, from about 30% to about 80% of the non-linear blocks are crosslinked with each other; from about 30% to about 70% of the non-linear blocks are crosslinked with each other; from about 30% to about 60% of the non-linear blocks are crosslinked with each other; from about 30% to about 50% of the non-linear blocks are crosslinked with each other; from about 30% to about 40% of the non-linear blocks are crosslinked with each other; from about 40% to about 80% of the non-linear blocks are crosslinked with each other; from about 40% to about 70% of the non-linear blocks are crosslinked with each other; from about 40% to about 60% of the non-linear blocks are crosslinked with each other; from about 40% to about 50% of the non-linear blocks are crosslinked with each other; from about 50% to about 80% of the non-linear blocks are crosslinked with each other; from about 50% to about 70% of the non-linear blocks are crosslinked with each other; from about 55% to about 70% of the non-linear blocks are crosslinked with each other; from about 50% to about 60% of the non-linear blocks are crosslinked with each other; from about 60% to about 80% of the non-linear blocks are crosslinked with each other; or from about 60% to about 70% of the non-linear blocks are crosslinked with each other.

In some embodiments, the organosiloxane block copolymers contained in the solid forms and solid compositions have a weight average molecular weight (M_(w)) of at least 20,000 g/mole, alternatively a weight average molecular weight of at least 40,000 g/mole, alternatively a weight average molecular weight of at least 50,000 g/mole, alternatively a weight average molecular weight of at least 60,000 g/mole, alternatively a weight average molecular weight of at least 70,000 g/mole, or alternatively a weight average molecular weight of at least 80,000 g/mole. In some embodiments, the organosiloxane block copolymers contained in the solid forms and solid compositions have a weight average molecular weight (M_(w)) of from about 20,000 g/mole to about 250,000 g/mole or from about 100,000 g/mole to about 250,000 g/mole, alternatively a weight average molecular weight of from about 40,000 g/mole to about 100,000 g/mole, alternatively a weight average molecular weight of from about 50,000 g/mole to about 100,000 g/mole, alternatively a weight average molecular weight of from about 50,000 g/mole to about 80,000 g/mole, alternatively a weight average molecular weight of from about 50,000 g/mole to about 70,000 g/mole, alternatively a weight average molecular weight of from about 50,000 g/mole to about 60,000 g/mole. In some embodiments, the organosiloxane block copolymers of the embodiments described herein have a number average molecular weight (M_(n)) of from about 15,000 to about 50,000 g/mole; from about 15,000 to about 30,000 g/mole; from about 20,000 to about 30,000 g/mole; or from about 20,000 to about 25,000 g/mole.

In some embodiments, the aforementioned organosiloxane block copolymers are isolated in a solid form, for example by casting films of a solution of the block copolymer in an organic solvent (e.g., benzene, toluene, xylene or combinations thereof) and allowing the solvent to evaporate. Under these conditions, the aforementioned organosiloxane block copolymers can be provided as solutions in an organic solvent containing from about 50 wt % to about 80 wt % solids, e.g., from about 60 wt % to about 80 wt %, from about 70 wt % to about 80 wt % or from about 75 wt % to about 80 wt % solids. In some embodiments, the solvent is toluene. In some embodiments, such solutions will have a viscosity of from about 1500 cSt to about 4000 cSt at 25° C., e.g., from about 1500 cSt to about 3000 cSt, from about 2000 cSt to about 4000 cSt or from about 2000 cSt to about 3000 cSt at 25° C.

Upon drying or forming a solid, the non-linear blocks of the block copolymer further aggregate together to form “nano-domains”. As used herein, “predominately aggregated” means the majority of the non-linear blocks of the organosiloxane block copolymer are found in certain regions of the solid composition, described herein as “nano-domains”. As used herein, “nano-domains” refers to those phase regions within the solid block copolymer compositions that are phase separated within the solid block copolymer compositions and possess at least one dimension sized from 1 to 100 nanometers. The nano-domains may vary in shape, providing at least one dimension of the nano-domain is sized from 1 to 100 nanometers. Thus, the nano-domains may be regular or irregularly shaped. The nano-domains may be spherically shaped, tubular shaped, and in some instances lamellar shaped.

In a further embodiment, the solid organosiloxane block copolymers as described above contain a first phase and an incompatible second phase, the first phase containing predominately the disiloxy units [R¹ ₂SiO_(2/2)] as defined above, the second phase containing predominately the trisiloxy units [R²SiO_(3/2)] as defined above, the non-linear blocks being sufficiently aggregated into nano-domains which are incompatible with the first phase.

When solid compositions are formed from the curable compositions of the organosiloxane block copolymer, which also contain an organosiloxane resin, as described above, the organosiloxane resin also predominately aggregates within the nano-domains.

The structural ordering of the disiloxy and trisiloxy units in the solid block copolymers of the present disclosure, and characterization of the nano-domains, may be determined explicitly using certain analytical techniques such as Transmission Electron Microscopic (TEM) techniques, Atomic Force Microscopy (AFM), Small Angle Neutron Scattering, Small Angle X-Ray Scattering, and Scanning Electron Microscopy.

Alternatively, the structural ordering of the disiloxy and trisiloxy units in the block copolymer, and formation of nano-domains, may be implied by characterizing certain physical properties of coatings resulting from the present organosiloxane block copolymers. For example, the present organosiloxane copolymers may provide coatings that have an optical transmittance of visible light greater than 95%. One skilled in the art recognizes that such optical clarity is possible (other than refractive index matching of the two phases) only when visible light is able to pass through such a medium and not be diffracted by particles (or domains as used herein) having a size greater than 150 nanometers. As the particle size, or domains further decreases, the optical clarity may be further improved. Thus, coatings derived from the present organosiloxane copolymers may have an optical transmittance of visible light of at least 95%, e.g., at least 96%; at least 97%; at least 98%; at least 99%; or 100% transmittance of visible light. As used herein, the term “visible light” includes light with wavelengths above 350 nm.

The advantage of the present resin-linear organopolysiloxanes block copolymers is that they can be processed several times, because the processing temperature (T_(processing)) is less than the temperature required to finally cure (T_(cure)) the organosiloxane block copolymer, i.e., T_(processing)<T_(cure). However the organosiloxane copolymer will cure and achieve high temperature stability when T_(processing) is taken above T_(cure). Thus, the present resin-linear organopolysiloxanes block copolymers offer the significant advantage of being “re-processable”in conjunction with the benefits typically associated with silicones, such as; hydrophobicity, high temperature stability, moisture/UV resistance.

In one embodiment, the solid compositions of the organosiloxane block copolymers may be considered as “melt processable”. In this embodiment, the solid compositions, such as a coating formed from a film of a solution containing the organosiloxane block copolymers, exhibit fluid behavior at elevated temperatures, that is upon “melting”. The “melt processable” features of the solid compositions of the organosiloxane block copolymers may be monitored by measuring the “melt flow temperature” of the solid compositions, that is when the solid composition demonstrates liquid behavior. The melt flow temperature may specifically be determined by measuring the storage modulus (G′), loss modulus (G″) and tan delta as a function of temperature storage using commercially available instruments. For example, a commercial rheometer (such as TA Instruments' ARES-RDA—with 2KSTD standard flexular pivot spring transducer, with forced convection oven) may be used to measure the storage modulus (G′), loss modulus (G″) and tan delta as a function of temperature. Test specimens (typically 8 mm wide, 1 mm thick) may be loaded in between parallel plates and measured using small strain oscillatory rheology while ramping the temperature in a range from 25° C. to 300° C. at 2° C./min (frequency 1 Hz). The flow onset may be calculated as the inflection temperature in the G′ drop (labeled FLOW), the viscosity at 120° C. is reported as a measure for melt processability and the cure onset is calculated as the onset temperature in the G′ rise (labeled CURE). Typically, the FLOW of the solid compositions will also correlate to the glass transition temperature of the non-linear segments (i.e., the resin component) in the organosiloxane block copolymer.

In some embodiments, the tan delta=1 is from about 3 to about 5 hours at 150° C., e.g., from about 3 to about 5 minutes at 150° C., from about 10 to about 15 minutes at 150° C., from about 10 to about 12 minutes at 150° C., from about 8 to about 10 minutes at 150° C., from about 30 minutes to about 2.5 hours at 150° C., from about 1 hour to about 4 hours at 150° C. or from about 2.5 hours to about 5 hours at 150° C.

In a further embodiment, the solid compositions may be characterized as having a melt flow temperature ranging from 25° C. to 200° C., alternatively from 25° C. to 160° C., or alternatively from 50° C. to 160° C.

It is believed that the melt processability benefits enables the reflow of solid compositions of the organosiloxane block copolymers around device architectures at temperatures below T_(cure), after an initial coating or solid is formed on the device. This feature is very beneficial to encapsulated various electronic devices.

In one embodiment, the solid compositions of the organosiloxane block copolymers may be considered as “curable”. In this embodiment, the solid compositions, such as a coating formed from a film of a solution containing the organosiloxane block copolymers, may undergo further physical property changes by further curing the block copolymer. As discussed above, the present organosiloxane block copolymers contain a certain amount of silanol groups. It is believed that the presence of these silanol groups on the block copolymer permit further reactivity, i.e., a cure mechanism. Upon curing, the physical properties of solid compositions may be further altered, as discussed in certain embodiments below.

Alternatively, the “melt processability” and/or cure of the solid compositions of the organosiloxane block copolymers may be determined by rheological measurements at various temperatures.

The solid compositions containing the organosiloxane block copolymers may have a storage modulus (G′) at 25° C. ranging from 0.01 MPa to 500 MPa and a loss modulus (G″) ranging from 0.001 MPa to 250 MPa, alternatively a storage modulus (G′) at 25° C. ranging from 0.1 MPa to 250 MPa and a loss modulus (G″) ranging from 0.01 MPa to 125 MPa, alternatively a storage modulus (G′) at 25° C. ranging from 0.1 MPa to 200 MPa and a loss modulus (G″) ranging from 0.01 MPa to 100 MPa.

The solid compositions containing the organosiloxane block copolymers may have a storage modulus (G′) at 120° C. ranging from 10 Pa to 500,000 Pa and a loss modulus (G″) ranging from 10 Pa to 500,000 Pa, alternatively a storage modulus (G′) at 120° C. ranging from 20 Pa to 250,000 Pa and a loss modulus (G″) ranging from 20 Pa to 250,000 Pa, alternatively a storage modulus (G′) at 120° C. ranging from 30 Pa to 200,000 Pa and a loss modulus (G″) ranging from 30 Pa to 200,000 Pa.

The solid compositions containing the organosiloxane block copolymers may have a storage modulus (G′) at 200° C. ranging from 10 Pa to 100,000 Pa and a loss modulus (G″) ranging from 5 Pa to 80,000 Pa, alternatively a storage modulus (G′) at 200° C. ranging from 20 Pa to 75,000 Pa and a loss modulus (G″) ranging from 10 Pa to 65,000 Pa, alternatively a storage modulus (G′) at 200° C. ranging from 30 Pa to 50,000 Pa and a loss modulus (G″) ranging from 15 Pa to 40,000 Pa.

The solid compositions may be further characterized by certain physical properties such as tensile strength and % elongation at break. The present solid compositions derived from the aforementioned organosiloxane block copolymers may have an initial tensile strength greater than 1.0 MPa, alternatively greater than 1.5 MPa, or alternatively greater than 2 MPa. In some embodiments, the solid compositions may have an initial tensile strength for from 1.0 MPa to about 10 MPa, e.g., from about 1.5 MPa to about 10 MPa, from about 2 MPa to about 10 MPa, from about 5 MPa to about 10 MPa or from about 7 MPa to about 10 MPa. The present solid compositions derived from the aforementioned organosiloxane block copolymers may have an initial % elongation at break (or rupture) greater than 40%, alternatively greater than 50%, or alternatively greater than 75%. In some embodiments, the solid compositions may have a % elongation at break (or rupture) of from about 20% to about 90%, e.g., from about 25% to about 50%, from about 20% to about 60%, from about 40% to about 60%, from about 40% to about 50%, or from about 75% to about 90%. As used herein, tensile strength and % elongation at break are measured according to ASTM D412.

In some embodiments, the solid compositions (e.g., solid curable film compositions) may be further characterized by improved “toughness”. As used herein, “toughness” refers to the “Trouser Tear strength” as measured by ASTM D624. The trouser tear strength of the solid compositions having improved toughness is greater than 0.5 kN/m, alternatively 0.75 kN/m, or alternatively greater than 1.00 kN/m. In some embodiments, the toughness is from about 0.575 kN/m to about 5.00 kN/m, e.g., 1 kN/m to about 4 kN/m, 2 kN/m to about 4 kN/m, or 0.2 kN/m to about 3 kN/m.

In some embodiments, the trouser tear strength is increased by at least 20%, relative to solid compositions lacking a stabilizer. In some embodiments, the trouser tear strength is increased by about 20% to about 50%, e.g., from about 20% to about 40%, from about 30% to about 50% or from about 25% to about 45% relative to solid compositions lacking a stabilizer.

The present disclosure further provides a process for preparing a curable composition comprising:

-   -   I) reacting         -   a) a linear organosiloxane having the formula

R¹ _(q)(E)_((3-q))SiO(R¹ ₂SiO_(2/2))_(n)Si(E)_((3-q))R¹ _(q),

-   -   -   -   where each R¹ is independently a C₁ to C₃₀ hydrocarbyl,             -   n is 10 to 400, q is 0, 1, or 2,             -   E is a hydrolyzable group containing at least one carbon                 atom, and

        -   b) an organosiloxane resin comprising at least 60 mole % of             [R²SiO_(3/2)]siloxy             -   units in its formula, where each R² is independently a                 C₁ to C₂₀ hydrocarbyl,

        -   in c) an organic solvent;

        -   to form a resin-linear organosiloxane block copolymer;             -   wherein the amounts of a) and b) used in step I are                 selected to provide the resin-linear organosiloxane                 block copolymer with 40 to 90 mole % of disiloxy units                 [R¹ ₂SiO_(2/2)] and 10 to 60 mole % of trisiloxy units                 [R²SiO_(3/2)], and             -   wherein at least 95 weight percent of the linear                 organosiloxane added in step I is incorporated into the                 resin-linear organosiloxane block copolymer,

    -   II) reacting the resin-linear organosiloxane block copolymer         from step I) to crosslink the trisiloxy units of the         resin-linear organosiloxane block copolymer sufficiently to         increase the average molecular weight (M_(w)) of the         resin-linear organosiloxane block copolymer by at least 50%;

    -   III) adding to the resin-linear organosiloxane block copolymer         from step II) a stabilizer to         -   enhance storage stability; and

    -   IV) optionally, removing the organic solvent.

The Linear Organosiloxane

Component a) in step I of the present process is a linear organosiloxane having the formula R¹ _(q)(E)_((3-q))SiO(R¹ ₂SiO_(2/2))_(n)Si(E)_((3-q)) R¹ _(g), where each R¹ is independently a C₁ to C₃₀ hydrocarbyl, the subscript “n” may be considered as the degree of polymerization (dp) of the linear organosiloxane and may vary from 10 to 400, the subscript “q” may be 0, 1, or 2, and E is a hydrolyzable group containing at least one carbon atom. While component a) is described as a linear organosiloxane having the formula R¹ _(q)(E)_((3-q))SiO(R¹ ₂SiO_(2/2))_(n)Si(E)_((3-q))R¹ _(g), one skilled in the art recognizes small amount of alternative siloxy units, such a T (R¹SiO_(3/2)) siloxy units, may be incorporated into the linear organosiloxane and still be used as component a). As such, the organosiloxane may be considered as being “predominately” linear by having a majority of D (R¹ ₂SiO_(2/2)) siloxy units. Furthermore, the linear organosiloxane used as component a) may be a combination of several linear organosiloxanes. Still further, the linear organosiloxane used as component a) may comprise silanol groups. In some embodiments, the linear organosiloxane used as component a) comprises from about 0.5 to about 5 mole % silanol groups, e.g., from about 1 mole % to about 3 mole %; from about 1 mole % to about 2 mole % or from about 1 mole % to about 1.5 mole % silanol groups.

R¹ in the above linear organosiloxane formula is independently a C₁ to C₃₀ hydrocarbyl. The hydrocarbon group may independently be an alkyl, aryl, or alkylaryl group. R¹ may be a C₁ to C₃₀ alkyl group, alternatively R¹ may be a C₁ to C₁₈ alkyl group. Alternatively R¹ may be a C₁ to C₆ alkyl group such as methyl, ethyl, propyl, butyl, pentyl, or hexyl. Alternatively R¹ may be methyl. R¹ may be an aryl group, such as phenyl, naphthyl, or an anthryl group. Alternatively, R¹ may be any combination of the aforementioned alkyl or aryl groups. Alternatively, R¹ is phenyl, methyl, or a combination of both.

E may be selected from any hydrolyzable group containing at least one carbon atom. In some embodiments, E is selected from an oximo, epoxy, carboxy, amino, amido group or combinations thereof. Alternatively, E may have the formula R¹C(═O)O—, R¹ ₂C═N—O—, or R⁴C═N—O—, where R¹ is as defined above, and R⁴ is hydrocarbyl. In one embodiment, E is H₃CC(═O)O-(acetoxy) and q is 1. In one embodiment, E is (CH₃)(CH₃CH₂)C═N—O-(methylethylketoxy) and q is 1.

In one embodiment, the linear organosiloxane has the formula (CH₃)_(q)(E)_((3-q))SiO[(CH₃)₂SiO_(2/2))]_(n)Si(E)_((3-q))(CH₃)_(q), where E, n, and q are as defined above.

In one embodiment, the linear organosiloxane has the formula (CH₃)_(q)(E)_((3-q))SiO[(CH₃)(C₆H₅)SiO_(2/2))]_(n)Si(E)_((3-q))(CH₃)_(q), where E, n, and q are as defined above.

Processes for preparing linear organosiloxanes suitable as component a) are known. In some embodiments, a silanol terminated polydiorganosiloxane is reacted with an “endblocking” compound such as an alkyltriacetoxysilane or a dialkylketoxime. The stoichiometry of the endblocking reaction is typically adjusted such that a sufficient amount of the endblocking compound is added to react with all the silanol groups on the polydiorganosiloxane. Typically, a mole of the endblocking compound is used per mole of silanol on the polydiorganosiloxane. Alternatively, a slight molar excess such as 1 to 10% of the endblocking compound may be used. The reaction is typically conducted under anhydrous conditions to minimize condensation reactions of the silanol polydiorganosiloxane. Typically, the silanol ended polydiorganosiloxane and the endblocking compound are dissolved in an organic solvent under anhydrous conditions, and allowed to react at room temperature, or at elevated temperatures (up to the boiling point of the solvent).

The Organosiloxane Resin

Component b) in the present process is an organosiloxane resin comprising at least 60 mole % of [R²SiO_(3/2)] siloxy units in its formula, where each R² is independently a C₁ to C₂₀ hydrocarbyl. The organosiloxane resin may contain any amount and combination of other M, D, and Q siloxy units, provided the organosiloxane resin contains at least 70 mole % of [R²SiO_(3/2)] siloxy units, alternatively the organosiloxane resin contains at least 80 mole % of [R²SiO_(3/2)] siloxy units, alternatively the organosiloxane resin contains at least 90 mole % of [R²SiO_(3/2)] siloxy units, or alternatively the organosiloxane resin contains at least 95 mole % of [R²SiO_(3/2)] siloxy units. In some embodiments, the organosiloxane resin contains from about 70 to about 100 mole % of [R²SiO_(3/2)] siloxy units, e.g., from about 70 to about 95 mole % of [R²SiO_(3/2)] siloxy units, from about 80 to about 95 mole % of [R²SiO_(3/2)] siloxy units or from about 90 to about 95 mole % of [R²SiO_(3/2)] siloxy units. Organosiloxane resins useful as component b) include those known as “silsesquioxane” resins.

Each R² is independently a C₁ to C₂₀ hydrocarbyl. R² may be an aryl group, such as phenyl, naphthyl, anthryl group. Alternatively, R² may be an alkyl group, such as methyl, ethyl, propyl, or butyl. Alternatively, R² may be any combination of the aforementioned alkyl or aryl groups. Alternatively, R² is phenyl or methyl.

The weight average molecular weight (M_(w)) of the organosiloxane resin is not limiting, but, in some embodiments, ranges from 1000 to 10,000, or alternatively 1500 to 5000 g/mole.

One skilled in the art recognizes that organosiloxane resins containing such high amounts of [R²SiO_(3/2)] siloxy units will inherently have a certain concentration of Si—OZ where Z may be hydrogen (i.e., silanol), an alkyl group (so that OZ is an alkoxy group), or alternatively OZ may also be any of the “E” hydrolyzable groups as described above. The Si—OZ content as a mole percentage of all siloxy groups present on the organosiloxane resin may be readily determined by ²⁹Si NMR. The concentration of the OZ groups present on the organosiloxane resin will vary, as dependent on the mode of preparation, and subsequent treatment of the resin. In some embodiments, the silanol (Si—OH) content of organosiloxane resins suitable for use in the present process will have a silanol content of at least 5 mole %, alternatively of at least 10 mole %, alternatively 25 mole %, alternatively 40 mole %, or alternatively 50 mole %. In other embodiments, the silanol content is from about 5 mole % to about 60 mole %, e.g., from about 10 mole % to about 60 mole %, from about 25 mole % to about 60 mole %, from about 40 mole % to about 60 mole %, from about 25 mole % to about 40 mole % or from about 25 mole % to about 50 mole %.

Organosiloxane resins containing at least 60 mole % of [R²SiO_(3/2)] siloxy units, and methods for preparing them, are known in the art. They are typically prepared by hydrolyzing an organosilane having three hydrolyzable groups on the silicon atom, such as a halogen or alkoxy group in an organic solvent. A representative example for the preparation of a silsesquioxane resin may be found in U.S. Pat. No. 5,075,103. Furthermore, many organosiloxane resins are available commercially and sold either as a solid (flake or powder), or dissolved in an organic solvent. Suitable, non-limiting, commercially available organosiloxane resins useful as component b) include; Dow Corning® 217 Flake Resin, 233 Flake, 220 Flake, 249 Flake, 255 Flake, Z-6018 Flake (Dow Corning Corporation, Midland Mich.).

One skilled in the art further recognizes that organosiloxane resins containing such high amounts of [R²SiO_(3/2)] siloxy units and silanol contents may also retain water molecules, especially in high humidity conditions. Thus, it is often beneficial to remove excess water present on the resin by “drying” the organosiloxane resin prior to reacting in step I. This may be achieved by dissolving the organosiloxane resin in an organic solvent, heating to reflux, and removing water by separation techniques (for example Dean Stark trap or equivalent process).

The amounts of a) and b) used in the reaction of step I are selected to provide the resin-linear organosiloxane block copolymer with 40 to 90 mole % of disiloxy units [R¹ ₂SiO_(2/2)] and 10 to 60 mole % of trisiloxy units [R²SiO_(3/2)]. The mole % of dilsiloxy and trisiloxy units present in components a) and b) may be readily determined using ²⁹Si NMR techniques. The starting mole % then determines the mass amounts of components a) and b) used in step I.

In some embodiments, the organosiloxane block copolymers comprise 40 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)], e.g., 50 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 60 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 65 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 70 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; or 80 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 40 to 80 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 40 to 70 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 40 to 60 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 40 to 50 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 50 to 80 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 50 to 70 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 50 to 60 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 60 to 80 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; 60 to 70 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)]; or 70 to 80 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)].

In some embodiments, the organosiloxane block copolymers comprise 10 to 60 mole percent trisiloxy units of the formula [R²SiO_(3/2)], e.g., 10 to 20 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 10 to 30 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 10 to 35 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 10 to 40 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 10 to 50 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 20 to 30 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 20 to 35 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 20 to 40 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 20 to 50 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 20 to 60 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 30 to 40 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 30 to 50 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 30 to 60 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; 40 to 50 mole percent trisiloxy units of the formula [R²SiO_(3/2)]; or 40 to 60 mole percent trisiloxy units of the formula [R²SiO_(3/2)].

The amount of components a) and b) selected should also ensure there is a molar excess of the silanol groups on the organosiloxane resin vs. amount of linear organosiloxane added. Thus, a sufficient amount of the organosiloxane resin should be added to potentially react with all the linear organosiloxane added in step I). As such, a molar excess of the organosiloxane resin is used. The amounts used may be determined by accounting for the moles of the organosiloxane resin used per mole of the linear organosiloxane.

As discussed above, the reaction affected in step I is a condensation reaction between the hydrolyzable groups of linear organosiloxane with the silanol groups on the organosiloxane resin. A sufficient amount of silanol groups needs to remain on the resin component of the formed resin-linear organosiloxane copolymer to further react in step II of the present process. In some embodiments, at least 10 mole %, alternatively at least 20 mole %, or alternatively at least 30 mole % silanol should remain on the trisiloxy units of the resin-linear organosiloxane copolymer as produced in step I of the present process. In some embodiments, from about 10 mole % to about 60 mole %, e.g., from about 20 mole % to about 60 mole %, or from about 30 mole % to about 60 mole %, should remain on the trisiloxy units of the resin-linear organosiloxane copolymer as produced in step I of the present process.

The reaction conditions for reacting the aforementioned (a) linear organosiloxane with the (b) organosiloxane resin are not limited. In some embodiments, reaction conditions are selected to effect a condensation type reaction between the a) linear organosiloxane and b) organosiloxane resin. Various non-limiting embodiments and reaction conditions are described in the Examples below. In some embodiments, the (a) linear organosiloxane and the (b) organosiloxane resin are reacted at room temperature. In other embodiments, (a) and (b) are reacted at temperatures that exceed room temperature and that range up to about 50, 75, 100, or even up to 150° C. Alternatively, (a) and (b) can be reacted together at reflux of the solvent. In still other embodiments, (a) and (b) are reacted at temperatures that are below room temperature by 5, 10, or even more than 10° C. In still other embodiments (a) and (b) react for times of 1, 5, 10, 30, 60, 120, or 180 minutes, or even longer. Typically, (a) and (b) are reacted under an inert atmosphere, such as nitrogen or a noble gas. Alternatively, (a) and (b) may be reacted under an atmosphere that includes some water vapor and/or oxygen. Moreover, (a) and (b) may be reacted in any size vessel and using any equipment including mixers, vortexers, stirrers, heaters, etc. In other embodiments, (a) and (b) are reacted in one or more organic solvents which may be polar or non-polar. Typically, aromatic solvents such as toluene, xylene, benzene, and the like are utilized. The amount of the organosiloxane resin dissolved in the organic solvent may vary, but typically the amount should be selected to minimize the chain extension of the linear organosiloxane or pre-mature condensation of the organosiloxane resin.

The order of addition of components a) and b) may vary. In some embodiments, the linear organosiloxane is added to a solution of the organosiloxane resin dissolved in the organic solvent. This order of addition is believed to enhance the condensation of the hydrolyzable groups on the linear organosiloxane with the silanol groups on organosiloxane resin, while minimizing chain extension of the linear organosiloxane or pre-mature condensation of the organosiloxane resin. In other embodiments, the organosiloxane resin is added to a solution of the linear organosiloxane dissolved in the organic solvent.

The progress of the reaction in step I, and the formation of the resin-linear organosiloxane block copolymer, may be monitored by various analytical techniques, such as GPC, IR, or ²⁹Si NMR. Typically, the reaction in step I is allowed to continue until at least 95 weight percent (e.g., at least 96%, at least 97%, at least 98%, at least 99% or 100%) of the linear organosiloxane added in step I is incorporated into the resin-linear organosiloxane block copolymer.

The second step of the present process involves further reacting the resin-linear organosiloxane block copolymer from step I) to crosslink the trisiloxy units of the resin-linear organosiloxane block copolymer to increase the molecular weight of the resin-linear organosiloxane block copolymer by at least 50%, alternatively by at least 60%, alternatively by 70%, alternatively by at least 80%, alternatively by at least 90%, or alternatively by at least 100%. In some embodiments, the second step of the present process involves further reacting the resin-linear organosiloxane block copolymer from step I) to crosslink the trisiloxy units of the resin-linear organosiloxane block copolymer to increase the molecular weight of the resin-linear organosiloxane block copolymer from about 50% to about 100%, e.g., from about 60% to about 100%, from about 70% to about 100%, from about 80% to about 100% or from about 90% to about 100%.

It is believed that reaction of step II crosslinks the trisiloxy blocks of the resin-linear organosiloxane block copolymer formed in step I, which will increase the average molecular weight of the block copolymer. The inventors also believe the crosslinking of the trisiloxy blocks provides the block copolymer with an aggregated concentration of trisiloxy blocks, which ultimately may help to form “nano-domains” in solid compositions of the block copolymer. In other words, this aggregated concentration of trisiloxy blocks may phase separate when the block copolymer is isolated in a solid form such as a film or cured coating. The aggregated concentration of trisiloxy block within the block copolymer and subsequent formation of “nano-domains” in the solid compositions containing the block copolymer, may provide for enhanced optical clarity of these compositions as well as the other physical property benefits associated with these materials.

The crosslinking reaction in Step II may be accomplished via a variety of chemical mechanisms and/or moieties. For example, crosslinking of non-linear blocks within the block copolymer may result from the condensation of residual silanol groups present in the non-linear blocks of the copolymer. Crosslinking of the non-linear blocks within the block copolymer may also occur between “free resin” components and the non-linear blocks. “Free resin” components may be present in the block copolymer compositions as a result of using an excess amount of an organosiloxane resin in step I of the preparation of the block copolymer. The free resin component may crosslink with the non-linear blocks by condensation of the residual silanol groups present on the non-linear blocks and on the free resin. The free resin may provide crosslinking by reacting with lower molecular weight compounds added as crosslinkers, as described below.

Step II of the present process may occur simultaneous upon formation of the resin-linear organosiloxane of step I, or involve a separate reaction in which conditions have been modified to affect the step II reaction. The step II reaction may occur in the same conditions as step I. In this situation, the step II reaction proceeds as the resin-linear organosiloxane copolymer is formed. Alternatively, the reaction conditions used for step I) are extended to further the step II reaction. Alternatively, the reaction conditions may be changed, or additional ingredients added to affect the step II reaction.

In some embodiments, the step II reaction conditions may depend on the selection of the hydrolyzable group (E) used in the starting linear organosiloxane. When (E) in the linear organosiloxane is an oxime group, it is possible for the step II reaction to occur under the same reaction conditions as step I. That is, as the linear-resin organosiloxane copolymer is formed in step I, it will continue to react via condensation of the silanol groups present on the resin component to further increase the molecular weight of the resin-linear organosiloxane copolymer. Not wishing to be bound by any theory, it is believed that when (E) is an oximo group, the hydrolyzed oximo group (for example methyl ethylketoxime) resulting from the reaction in step I may act as a condensation catalyst for the step II reaction. As such, the step II reaction may proceed simultaneously under the same conditions for step I. In other words, as the resin-linear organosiloxane copolymer is formed in step I, it may further react under the same reaction conditions to further increase its molecular weight via a condensation reaction of the silanol groups present on the resin component of the copolymer. However, when (E) on the linear organosiloxane is an acetoxy group, the resulting hydrolyzed group (acetic acid), does not sufficiently catalyze the step II) reaction. Thus, in this situation the step II reaction may be enhanced with a further component to affect condensation of the resin components of the resin-linear organosiloxane copolymer, as described in the embodiment below.

In one embodiment of the present process, an organosilane having the formula R⁵ _(q)SiX_(4-q) is added during step II), where R⁵ is a C₁ to C₈ hydrocarbyl or a C₁ to C₈ halogen-substituted hydrocarbyl, X is a hydrolyzable group, and q is 0, 1, or 2. R⁵ is a C₁ to C₈ hydrocarbyl or a C₁ to C₈ halogen-substituted hydrocarbyl, or alternatively R⁵ is a C₁ to C₈ alkyl group, or alternatively a phenyl group, or alternatively R⁵ is methyl, ethyl, or a combination of methyl and ethyl. X is any hydrolyzable group, alternatively X may be E, as defined above, a halogen atom, hydroxyl (OH), or an alkoxy group. In one embodiment, the organosilane is an alkyltriacetoxysilane, such as methyltriacetoxysilane, ethyltriacetoxysilane, or a combination of both. Commercially available representative alkyltriacetoxysilanes include ETS-900 (Dow Corning Corp., Midland, Mich.). Other suitable, non-limiting organosilanes useful in this embodiment include; methyl-tris(methylethylketoxime)silane (MTO), methyl triacetoxysilane, ethyl triacetoxysilane, tetraacetoxysilane, tetraoximesilane, dimethyl diacetoxysilane, dimethyl dioximesilane, methyl tris(methylmethylketoxime) silane.

The amount of organosilane having the formula R⁵ _(q)SiX_(4-q) when added during step II) varies, but should be based on the amount of organosiloxane resin used in the process. The amount of silane used should provide a molar stoichiometry of 2 to 15 mole % of organosilane per moles of Si on the organosiloxane resin. Furthermore, the amount of the organosilane having the formula R⁵ _(q)SiX_(4-q) added during step II) is controlled to ensure a stoichiometry that does not consume all the silanol groups on the organosiloxane block copolymer. In one embodiment, the amount of the organosilane added in step II is selected to provide an organosiloxane block copolymer containing 0.5 to 35 mole percent of silanol groups [≡SiOH].

Step III in the present process involves adding to the resin-linear organosiloxane block copolymer from step II) a stabilizer to enhance storage stability. The stabilizer and amounts used in step III are the same as described above.

Step IV of the present process is optional, and involves removing the organic solvent used in the reactions of steps I and II. The organic solvent may be removed by any known techniques, but typically involves heating the resin-linear organosiloxane copolymer compositions at elevated temperature, either at atmospheric conditions or under reduced pressures. In some embodiments, not all of the solvent is removed. In this embodiment, at least 20%, at least 30%, at least 40%, or at least 50% of the solvent is removed, e.g., at least 60%, at least 70%, at least 75%, at least 80% or at least 90% of the solvent is removed. In some embodiments, less than 20% of the solvent is removed, e.g., less than 15%, less than 10%, less than 5% or 0% of the solvent is removed. In other embodiments, from about 20% to about 100% of the solvent is removed, e.g., from about 30% to about 90%, from about 20% to about 80%, from about 30 to about 60%, from about 50 to about 60%, from about 70 to about 80% or from about 50% to about 90% of the solvent is removed.

The present disclosure further provides a method of improving the toughness of a solid curable film composition of a resin linear organopolysiloxane comprising adding to the composition a stabilizer selected from an alkaline earth metal salt, a metal chelate, or phenyl boronic acid.

Embodiments of the invention described and claimed herein are not to be limited in scope by the specific embodiments herein disclosed, since these embodiments are intended as illustration of several aspects of the disclosure. Any equivalent embodiments are intended to be within the scope of this disclosure. Indeed, various modifications of the embodiments in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.

The Abstract is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

EXAMPLES

The following examples are included to demonstrate specific embodiments of the invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. All percentages are in wt. %. All measurements were conducted at 23° C. unless indicated otherwise.

Characterization Techniques ²⁹Si and ¹³C NMR Spectrometry

NMR samples of resin linear products were prepared by weighing ˜3 grams of solvent free resin linear (prepared by drying sample overnight at room temperature), 1 g of CDCl₃, and 4 grams of 0.04 M Cr(acac)₃ solution in CDCl₃ into a vial and mixing thoroughly. Samples were then transferred into a silicon-free NMR tube. Spectra were acquired using a Varian Mercury 400 MHz NMR. NMR samples of other materials such as 217 Flake and silanol terminated PDMS were prepared by diluting 4 g of sample into 4 grams of 0.04 M Cr(acac)₃ solution in CDCl₃.

¹³C NMR experiments were performed in the following manner. Samples were placed into 16 mm glass NMR tubes. A 5 mm NMR tube was placed inside the 16 mm tube and filled with lock solvent. 13C DEPT NMR was acquired in 12 or 20 minute signal averaging blocks. Data was acquired on a Varian Inova NMR spectrometer with a 1H operational frequency of 400 MHz.

Silanol content of resin linear products was calculated from the integration values of the T(Ph,OZ) and T(Ph,OZ2) regions in the ²⁹Si NMR spectrum. T(Alkyl) groups were considered fully condensed (assumption) and subtracted from the T(Ph,OZ) region. The T(Alkyl) content was calculated by multiplying the integration value of D(Me₂) from ²⁹Si NMR by the fraction (moles Si of coupling agent/moles Si of PDMS used in the synthesis formulation). Isopropoxy from 217 Flake was not subtracted out of the OZ values due to its low concentration. Therefore it was assumed that total OZ=total OH.

GPC Analysis

Samples were prepared in certified THF at 0.5% w/v concentration, filtered with a 0.45 μm PTFE syringe filter, and analyzed against polystyrene standards. The relative calibration (3rd order fit) used for molecular weight determination was based on 16 polystyrene standards ranging in molecular weights from 580 to 2,320,000 Daltons. The chromatographic equipment consisted of a Waters 2695 Separations Module equipped with a vacuum degasser, a Waters 2410 differential refractometer and two (300 mm×7.5 mm) Polymer Laboratories Mixed C columns (molecular weight separation range of 200 to 3,000,000) preceded by a guard column. The separation was performed using certified grade THF programmed to flow at 1.0 mL/min., injection volume was set at 100 μL and columns and detector were heated to 35° C. Data collection was 25 minutes and processing was performed using Atlas/Cirrus software.

To determine free resin content, the free resin peak at lower molecular weight was integrated to get the area percent.

Rheology Analysis

A commercially available rheometer from TA Instruments (ARES-RDA with 2KSTD standard flexular pivot spring transducer, TA Instruments, New Castle, Del. 19720) with forced convection oven was used to measure the storage modulus (G′), loss modulus (G″) and tan delta as a function of temperature. Test specimens (typically 8 mm wide, 1 mm thick) were loaded in between parallel plates and measured using small strain oscillatory rheology while ramping the temperature in a range from 25° C. to 300° C. at 2° C./min (frequency 1 Hz).

To characterize the copolymers, the flow onset was calculated as the inflection temperature in the G′ drop (labeled FLOW), the viscosity at 120° C. will be reported as a measure for melt processability and the cure onset was calculated as the inflection temperature in the G′ rise (labeled CURE).

A typical rheology curve on an organosiloxane copolymer is shown in FIG. 1. The results of the rheological evaluations of the representative examples disclosed herein, are summarized further below in Table 1.

Tear Strength

Tear strengths were evaluated according to ASTM D624. Specimens were die cut from cured films typically measuring 1-2 mm in thickness. If testing Type B or Type C geometries three specimens were utilized. If testing type T (trouser), one to three specimens were prepared depending on the amount of sample film available. Before testing no special storage considerations were taken as the materials were not expected to be significantly affected by small changes in temperature or humidity. Specimens were tested at ambient temperature and humidity with an Instron universal test machine utilizing Bluehill 2 software. For type B and C specimens the test speed used was 500 mm/min and specimens were pulled to failure. Median peak force/thickness was reported. For type T (trouser) specimens a pulling speed of 50 mm/min was used and specimens were pulled until the tear force was seen to level off or until failure occurred. After testing the beginning and ending points of the level region of the force curve were identified visually. Then the analyzing function of the software was used to calculate the average tear force/thickness within the identified region. If more than one specimen was tested the median reading was reported.

Optical Clarity

Optical clarity was evaluated as the % transmission of light at wavelengths from about 350-1000 nanometers, measured through 1 mm thick samples of cast sheets of the present compositions. Samples having a % transmittance of at least 95% were considered to be optically clear.

Example 1

A 5 L 3 neck round bottom flask was loaded with a phenylsilsesquioxane hydrolyzate (Dow Corning 217 Flake, 280.0 g, 2.044 moles Si) and toluene (Fisher Scientific, 1000.0 g). The flask was equipped with a thermometer, Teflon stir paddle, and a Dean Stark apparatus attached to a water-cooled condenser. A nitrogen blanket was applied. The Dean Stark was prefilled with toluene. An oil bath was used for heating. The reaction mixture was heated at reflux for 30 min. After cooling the reaction mixture to 108° C., a solution of diacetoxy terminated PDMS was added. The diacetoxy terminated PDMS was prepared by capping a 184 dp silanol terminated PDMS (720.0 g, 9.690 moles Si) dissolved in toluene (500.0 g) with a 50/50 wt % mixture of methyl and ethyl triacetoxysilanes (23.88 g, 0.1028 moles Si). The solution was mixed at room temperature for 30 minutes under a nitrogen blanket. The diacetoxy terminated PDMS was added quickly to the phenylsilsesquioxane hydrolyzate solution at 108° C. The reaction mixture was heated at reflux for 2 hrs. At this stage a 50/50 wt % mixture of methyl and ethyl triacetoxysilanes (34.27 g. 0.147 moles Si) was added at 108° C. and the mixture was refluxed for 1 hr. Deionized water (158 mL) was added and the aqueous phase removed through azeotropic distillation using a Dean Stark apparatus. This procedure was repeated 2 more times to reduce the acetic acid concentration. Product solution was pressure filtered through a 5.0 μm filter. Cast sheets (made by pouring the solution in a chase and evaporating the solvent overnight at room temperature) were optically clear.

A 32 oz. jar was loaded with 500.0 g (200.0 g solids) of the above product in a toluene solution and calcium chloride (25.0 g). The solution was mixed for several hours and then left for 5 days at room temperature. The material was pressure filtered through a 5.0 μm filter. Cast sheets were optically clear.

Example 2

A 2 L 3 neck round bottom flask was loaded with a phenylsilsesquioxane hydrolyzate (Dow Corning 217 Flake, 58.8 g, 0.429 moles Si) and toluene (Fisher Scientific, 210.0 g). The flask was equipped with a thermometer, Teflon stir paddle, and a Dean Stark apparatus attached to a water-cooled condenser. A nitrogen blanket was applied. The Dean Stark was prefilled with toluene. An oil bath was used for heating. The reaction mixture was heated at reflux for 30 min. After cooling the reaction mixture to 108° C., a solution of diacetoxy terminated PDMS was added. The diacetoxy terminated PDMS was prepared by capping a 184 dp silanol terminated PDMS (130.2 g, 1.752 moles Si) and a 45 dp silanol terminated PDMS (21.0 g, 0.282 moles Si) dissolved in toluene (97.31 g) with a 50 wt % solution of 50/50 wt % mixture of methyl and ethyl triacetoxysilanes (15.37 g, 0.0331 moles Si) in toluene. The solution was mixed at room temperature for 2 hrs. under a nitrogen blanket. The diacetoxy terminated PDMS was added quickly to the phenylsilsesquioxane hydrolyzate solution at 108° C. The reaction mixture was heated at reflux for 2 hrs. At this stage a 50 wt % solution in toluene of a 50/50 wt % mixture of methyl and ethyl triacetoxysilanes (7.98 g, 0.0172 moles Si) was added at 108° C. and the mixture was refluxed for 1 hr. Deionized water (36 mL) was added and the aqueous phase removed through azeotropic distillation using a Dean Stark apparatus. This procedure was repeated 2 more times to reduce the acetic acid concentration. Product solution was pressure filtered through a 5.0 μm filter. Cast sheets (made by pouring the solution in a chase and evaporating the solvent overnight at room temperature) were optically clear.

Calcium chloride treatment was done in the same way as for Example 1, but scaled accordingly.

Example 3

A 2 L 3 neck round bottom flask was loaded with a phenylsilsesquioxane hydrolyzate (Dow Corning 217 Flake, 84.0 g, 0.613 moles Si) and toluene (Fisher Scientific, 210.0 g). The flask was equipped with a thermometer, Teflon stir paddle, and a Dean Stark apparatus attached to a water-cooled condenser. A nitrogen blanket was applied. The Dean Stark was prefilled with toluene. An oil bath was used for heating. The reaction mixture was heated at reflux for 30 min. After cooling the reaction mixture to 108° C., a solution of diacetoxy terminated PDMS was added. The diacetoxy terminated PDMS was prepared by capping a 184 dp silanol terminated PDMS (63.0 g, 0.848 moles Si) and a 45 dp silanol terminated PDMS (63.0 g, 0.845 moles Si) dissolved in toluene (93.64 g) with a 50 wt % solution of 50/50 wt % mixture of methyl and ethyl triacetoxysilanes (22.72 g, 0.0489 moles Si) in toluene. The solution was mixed at room temperature for 2 hrs. under a nitrogen blanket. The diacetoxy terminated PDMS was added quickly to the phenylsilsesquioxane hydrolyzate solution at 108° C. The reaction mixture was heated at reflux for 2 hrs. Deionized water (35 mL) was added and the aqueous phase removed through azeotropic distillation using a Dean Stark apparatus. This procedure was repeated 2 more times to reduce the acetic acid concentration. Product solution was pressure filtered through a 5.0 μm filter. Cast sheets (made by pouring the solution in a chase and evaporating the solvent overnight at room temperature) were optically clear.

Calcium chloride treatment was done in the same way as for Example 1, but scaled accordingly.

Shelf stability was determined by measuring the time needed for the compositions to gel at 40° C. The results of the shelf aging studies for the resin-linear compositions of Examples 1-3 are summarized in Table 1.

TABLE 1 Gel Time (days) Example # Resin Linear Composition at 40° C. 1 28 wt % phenylsilsequioxane + 10 72 wt % 184 dp polydimethylsiloxane 1 + CaCl₂ 60 2 28 wt % phenylsilsequioxane + 5 62 wt % 184 dp polydimethylsiloxane + 10 wt % 45 dp polydimethylsiloxane 2 + CaCl₂ >72 3 40 wt % phenylsilsequioxane + 5 30 wt % 184 dp polydimethylsiloxane + 30 wt % 45 dp polydimethylsiloxane 3 + CaCl₂ >72

Example 4 Reference

A 1 L 3 neck round bottom flask was loaded with a phenylsilsesquioxane hydrolyzate (Dow Corning 217 Flake, 51.2 g, 0.374 moles Si) and toluene (Fisher Scientific, 160.0 g). The flask was equipped with a thermometer, Teflon stir paddle, and a Dean Stark apparatus attached to a water-cooled condenser. A nitrogen blanket was applied. The Dean Stark was prefilled with toluene. An oil bath was used for heating. The reaction mixture was heated at reflux for 30 min. After cooling the reaction mixture to 108° C., a solution of diacetoxy terminated PDMS was added. The diacetoxy terminated PDMS was made according to Example 2 using toluene (76.11 g), 184 dp silanol terminated PDMS (Gelest DMS-527, 108.8 g, 1.46 moles Si), and a 50 wt % solution of ETS-900 in toluene (Dow Corning, 7.79 g, 0.0168 moles Si). The diacetoxy terminated PDMS was added quickly to the phenylsilsesquioxane hydrolyzate solution at 108° C. The reaction mixture was heated at reflux for 2 hrs. At this stage a 50 wt % solution of ETS-900 in toluene (Dow Corning, 12.6 g, 0.0271 moles Si) was added and the mixture was refluxed for 1 hr. Deionized water (30 mL) was added and the aqueous phase removed through azeotropic distillation using a Dean Stark apparatus. This procedure was repeated 2 more times to reduce the acetic acid concentration. Cast sheets (made by pouring the solution in a chase and evaporating the solvent overnight at room temperature) were optically clear. The resulting sheet was a grabby elastomer at room temperature. Product Mw=144,000 (excludes free resin), OZ=6.56 mole %.

Examples 5-12

A vial was loaded with 20 g of the organosiloxane polymer from Example 4 (8 g solids). To this solution, the appropriate amount of the metal acetyl acetonate was added to reach the desired final ppm of metal in respect to resin-linear solids. To illustrate: for Example 10 for Mn, 2.08 g of Mn(acac) solution was added (962 ppm Mn in toluene). The solution was mixed at room temperature for 24 h. Sheets were cast at room temperature and the solvent was allowed to evaporate overnight. More details are below:

Materials: Resin-Linear Example 4

Metal Solutions Li, Mg, Al, Ni, V, Mn, Zr

(Concentrations Given Below) Equipment:

4 oz bottles

Parafilm

Mixing Wheel

Adhesive Al-backed Teflon release-liner

Tensile Dye C and Trouser Tear Dye

Instron

Method:

Mix all resin-linear+metal solutions at the following quantities:

Example 5 Al-250 ppm-AcAc

A bottle was loaded with:

35.0 g of the Resin Linear copolymer of Example 4 (14.0 g solids) 3.73 g of Al(AcAc) solution (938 ppm Al, in toluene)

Example 6 Li-250 ppm-AcAc

A bottle was loaded with:

35.0 g of the Resin Linear copolymer of Example 4 (14.0 g solids) 3.65 of Li(AcAc) solution (962 ppm Li, 60/40 wt % toluene/MeOH)

Example 7 V-250 ppm-AcAc

A bottle was loaded with:

35.0 g of the Resin Linear copolymer of Example 4 (14.0 g solids) 1.46 g of V(AcAc) solution (2400 ppm V, 60/40 wt % toluene/MeOH)

Example 8 Ni-250 ppm-AcAc

A bottle was loaded with:

35.0 g of the Resin Linear copolymer of Example 4 (14.0 g solids) 1.06 g of Ni(AcAc) solution (3315 ppm Ni, 60/40 wt % toluene/MeOH)

Example 9 Zr-250 ppm-AcAc

A bottle was loaded with:

35.0 g of the Resin Linear copolymer of Example 4 (14.0 g solids) 2.93 g of Zr(AcAc) solution (1197 ppm Zr, 60/40 wt % toluene/MeOH)

Example 10 Mn-250 ppm-AcAc

A bottle was loaded with:

35.0 g of the Resin Linear copolymer of Example 4 (14.0 g solids) 3.65 g of Mn(AcAc) solution (962 ppm Mn, toluene)

Example 11 Mg-250 ppm-AcAc

A bottle was loaded with:

35.0 g of the Resin Linear copolymer of Example 4 (14.0 g solids) 5.36 g of Mg(AcAc) solution (654 ppm Mg, 60/40 wt % toluene/MeOH)

Example 12 Mg-500 ppm-AcAc

A bottle was loaded with:

35.0 g of the Resin Linear copolymer of Example 4 (14.0 g solids) 4.89 g of Mg(AcAc) solution (1432 ppm Mg, 60/40 wt % toluene/MeOH)

Examples 5-12 demonstrate how formulations containing metal chelates have delayed onset or improved shelf stability, as measured by rheology. The table below shows values for the temperature and viscosity at the minimum in a viscosity vs. temperature plot (at 2° C./min). Higher temperatures and/or lower viscosities indicate postponed cure:

Metal in Metal(AcAc), T at viscosity Viscosity ppm Metal/copolymer minimum, minimum, Example solids ° C. kPa · s 4 none 135 84 5 250 ppm Al 154 55 6 250 ppm Li 168 39 7 250 ppm V 168 29 8 250 ppm Ni 178 18 9 250 ppm Zr 180 19 10 250 ppm Mn 177 15 1 250 ppm Ca 190 11 11 250 ppm Mg 179 14 12 500 ppm Mg 180 15

Improvements in toughness (trouser tear values all greater than the control (Example 4) were also seen with addition of metal AcAc's:

Peak Tensile Elongation Young's Trouser AcAc Strength at break Modulus Tear Example additive (MPa) (%) (MPa) (kN/m) 4 none 4.61 309 1.75 0.37 6 Li-250 ppm- 3.25 334 1.05 0.83 AcAc 5 Al-250 ppm- 4.08 271 1.75 0.62 AcAc 11 Mg-250 ppm- 3.25 621 0.77 1.54 AcAc 12 Mg-500 ppm- 2.59 403 0.83 1.57 AcAc 8 Ni-250 ppm- 3.59 632 0.77 1.83 AcAc 7 V-250 ppm- 3.72 480 0.90 1.20 AcAc 10 Mn-250 ppm- 3.37 566 0.77 1.41 AcAc 9 Zr-250 ppm- 2.73 485 0.84 1.59 AcAc

Examples 13-16 Subject Addition of Phenylboronic Acid to Resin Linear

-   Objective: Determine the effects of different amounts of     phenylboronic acid on the properties of resin-linears.

Materials:

acetoxy-based resin-linear of Example 1 before adding CaCl₂

Phenylboronic Acid: PhB(OH)₂

-   -   Ethanol     -   Toluene

Equipment:

-   -   4 oz bottles     -   Mixing Wheel     -   Al-backed teflon liner     -   Rheometer     -   Oven     -   Tensile Dye C     -   Trouser Tear Dye     -   Small “dogbone” dye (4.5 cm long; 2.5 mm at center)     -   Instron

Method:

-   -   1. A PhB(OH)₂ solution was made at approximately 25 wt % solids         in a 50/50 Toluene/EtOH mix by weighing 3.0843 g of PhB(OH)₂         into a vial and adding 4.6324 g toluene and 4.611 g ethanol.     -   2. Approximately 45 g of the resin-linear solution Example 1 was         added to four bottles (see table).     -   3. To the control, 1 g of ethanol and 1 g of toluene were added         to be sure ethanol alone does not affect the resin-linear         properties.     -   4. Different amounts of the PhB(OH)₂ solution were added to the         remaining three bottles, targeting a 1/10 (Example 14), ¼,         (Example 15) and ½ (Example 16) mole ratio of the PhB acid OH's         to the OZ content of Example 1.     -   5. Bottles were capped and placed on the mixing wheel for 3         hours.     -   6. Sheets were cast in 5″×5″ boats made from the Al-backed liner         and allowed to evaporate overnight.     -   7. 1.5″ square samples of each sheet were taken for 8 mm         parallel plate rheology and “small dogbone” tensile testing.     -   8. The remainders of the sheets were then cured at 160° C. for 3         hours before taking three Dye C dogbone samples and two trouser         tear samples for testing.

Improvements in toughness were also seen upon addition of phenyl boronic acid to the resin-linear copolymers, as summarized in the table below.

Cure Peak Temp & Tensile Young's Trouser time Strength Elongation Mod Tear Example T2 t2 (MPa) at break % (MPa) (kN/m) 13 = 160 3 hr 4.04 339 1.415 0.61 Example 1 14 160 3 hr 3.82 478 0.946 1.11 15 160 3 hr 2.87 559 1.007 1.52 16 160 3 hr 2.54 472 0.997 1.50

Example 17

A 1 L cylindrical four-neck flask with Teflon baffles was charged with toluene (148.21 g); and 217 flake phenyl-T resin (180.00 g, 1.318 moles Si). The flask was equipped with a thermometer; glass stir shaft with dual set of blades; and a Dean Stark apparatus attached to a water-cooled condenser. A nitrogen blanket was applied; the Dean Stark apparatus was prefilled with toluene; and a heating mantle was used for heating. The flask was heated at reflux for 30 minutes and 0.15 ml of water was removed. The flask was allowed to cool to 108° C.

A toluene solution of silanol terminated PhMe siloxane (338.46 g solution=220.00 g siloxane, 1.613 moles Si) was capped with 50/50 methyl triacetoxy silane (MTA)/ethyl triacetoxy silane (ETA) (4.70 g, 0.0207 moles Si) in a glove box (same day) under nitrogen by adding 50/50 MTA/ETA to the silanol terminated PhMe siloxane and mixing at room temperature for 1 hour.

The MTA/ETA-capped PhMe siloxane solution was added to the 217 flake solution quickly at 108° C. The reaction mixture was heated at reflux for 2 hrs. and 2.25 mL water was removed. The reaction mixture was allowed to come to room temperature (approximately 25° C.) and was stirred at room temperature overnight. The following day, the reaction mixture was heated to 106° C. and 50/50 MA/ETA (31.46 g, 0.138 moles) was added. The reaction mixture was heated to reflux in about 5 minutes, held at reflux for an hour, and 1.20 mL of water was removed. The following process was repeated twice: the reaction mixture was cooled to 90° C. and then deionized water (42.89 g) was added. The water was then removed via azeotropic distillation over 1.5 hrs. Total amount of water removed was 101.6 g. Volatiles (135.6 g) were distilled off to increase the solids content. The reaction mixture was then allowed to come to room temperature and was stirred overnight. The following day the reaction mixture was heated to reflux in 35 min, and then held at reflux for 2 hrs. Amount of water collected in Dean Stark apparatus was 0.4 mL. The reaction mixture was allowed to cool to room temperature and then pressure filtered through a 5.0 μm filter. Cast sheets (made by pouring the solution in a chase and evaporating the solvent overnight at room temperature) were optically clear.

A 32 oz. jar was charged with 500.0 g (375.0 g solids) of the product produced by the method described above as a solution in toluene, toluene (20 mL), and 150 ppm Al(acac)₃. The solution was mixed for several hours and then left for 5 days at room temperature. The viscosity of the solution at 25° C. was between 2,000 to 3,000 CSt. The material was pressure filtered through a 5.0 μm filter. Cast sheets were optically clear. The G′ at minimum determined for the sheets was between 0.5 to 5 kPa roughly, e.g., about 1.5 kPa. The time to gelation as defined by tan delta=1 was 8-15 min at 150° C. After cure with Al(AcAc)₃, tensile properties are: tensile strength at break 5-10 Mpa; elongation at break 25-50%; modulus 150 Mpa; and trouser tear strength 3 kN/m.

Example 18-20 Example using Ph₂MeSiOH/45 wt % Ph-T-PhMe and Al(acac)₃

Ph₂MeSiOH T at viscosity Viscosity Al(acac)₃ level (wt % vs. minimum, minimum, Example ppm total solids) ° C. Pa · s 18 150 0 165 387 19 150 0.5 185 25 20 150 2.5 185 22

Resin-linear: 45 wt % 217 Flake; 55 wt % 126 dp PhMe siloxane (1.22 mole % SiOH).

Reagents:

Phenyl-T Resin: FW=136.6 g/mole Si.

126 dp silanol terminated PhMe Siloxane—65% in toluene; FW=136.4 g/mol Si, 1.22 mol % SiOH.

Toluene.

ETS900 (methyl triacetoxysilane/ethyl triacetoxysilane (MTA/ETA) 5/5 wt/wt ratio), Avg. FW=227.3 g/mol Si.

Procedure:

A 12 L 3 neck round bottom flask was charged with toluene (1482.05 g) and 217 flake (1800.0 g, 13.18 moles Si). The flask was equipped with a thermometer, teflon stir paddle, and a Dean Stark apparatus attached to a water-cooled condenser. A nitrogen blanket was applied. The Dean Stark apparatus was prefilled with toluene, and a heating mantle was used for heating. The flask was heated at reflux for 30 minutes and 8.17 g of water were removed. The flask was cooled to 108° C. (pot temperature).

A solution of silanol terminated PhMe siloxane (3384.62 g solution=2200.0 g siloxane, 16.13 moles Si) was capped with methyl triacetoxysilane/ethyl triacetoxysilane (MTA/ETA) 5/5 wt/wt ratio (46.96 g, 0.207 moles Si). It was prepared in a glove box (same day) under nitrogen by adding MTA/ETA to the siloxane and mixing at room temperature for 1 hour. The siloxane solution was added to the 217 flake solution quickly at 108° C. The reaction mixture was heated at reflux for 2 hrs and 14.66 g of water were removed. The reaction mixture was cooled to 108° C. Barry ETS900 (314.49 g, 1.384 moles) was added. The reaction mixture was heated at reflux for 1 hour and 0.56 g of water were removed.

The following procedure was repeated twice:

The reaction mixture was cooled to 90° C. and then added deionized water (430.0 g). The reaction mixture was heated to reflux and removed water via azeotropic distillation. Total amount of aqueous phase removed: 1045.9 g. Distilled off some volatiles (1331.4 g) to increase the solids content. Final pot temperature: 118° C. The reaction mixture was cooled to room temperature.

A 32 oz. jar was charged with 500.0 g (375.0 g solids) of the product produced by the method described above as a solution in toluene, toluene (20 mL), and 150 ppm Al(acac)₃, followed by the addition of the amount of Ph₂MeSiOH listed in the table above. The solution was mixed for several hours and then left for 5 days at room temperature. The viscosity of the solution was as listed in the table above. The material was pressure filtered through a 5.0 μm filter. Cast sheets were optically clear. 

1. A curable composition comprising: i) an organosiloxane block copolymer comprising: 40 to 90 mole percent disiloxy units of the formula [R¹ ₂SiO_(2/2)], 10 to 60 mole percent trisiloxy units of the formula [R²SiO_(3/2)], 0.5 to 35 mole percent silanol groups [≡SiOH]; wherein: R¹ is independently a C₁ to C₃₀ hydrocarbyl, R² is independently a C₁ to C₂₀ hydrocarbyl; wherein: the disiloxy units [R¹ ₂SiO_(2/2)] are arranged in linear blocks having an average of from 10 to 400 disiloxy units [R¹ ₂SiO_(2/2)] per linear block, the trisiloxy units [R²SiO_(3/2)] are arranged in non-linear blocks having a molecular weight of at least 500 g/mol, and at least 30% of the non-linear blocks are crosslinked with each other, each linear block is linked to at least one non-linear block; and the organosiloxane block copolymer has a weight average molecular weight (M_(w)) of at least 20,000 g/mole; and ii) a stabilizer, wherein the stabilizer comprises alkaline earth metal salt, a metal chelate, a boron compound, a silicon-containing small-molecule or combinations thereof.
 2. (canceled)
 3. (canceled)
 4. The curable composition of claim 1, wherein the boron compound comprises a boronic acid.
 5. (canceled)
 6. The curable composition of claim 4, wherein the boronic acid comprises phenyl boronic acid.
 7. The curable composition of claim 1, wherein the alkaline earth metal salt comprises calcium chloride.
 8. The curable composition of claim 1, wherein the metal chelate comprises a metal acetylacetonate complex.
 9. The curable composition of claim 8, wherein the metal is Al, Li, V, Ni, Zr, Mn, Ca, or Mg.
 10. The curable composition of claim 1, wherein R² is phenyl.
 11. The curable composition of claim 1, wherein R¹ is methyl or phenyl.
 12. The curable composition of claim 1, wherein the disiloxy units have the formula [(CH₃)(C₆H₅)SiO_(2/2)].
 13. The curable composition of claim 1, wherein the disiloxy units have the formula [(CH₃)₂SiO_(2/2)].
 14. The curable composition of claim 1, wherein the stabiliser is a silanol condensation enhancing agent.
 15. A solid film composition comprising the curable composition of claim
 1. 16. The solid film composition of claim 15, wherein the film has a trouser tear of at least 0.75 kN/m.
 17. The solid film compositions of claim 15, wherein the solid composition has an optical transmittance of at least 95%.
 18. A process for preparing a curable composition comprising: I) reacting a) a linear organosiloxane having the formula: R¹ _(q)(E)_((3-q))SiO(R¹ ₂SiO_(2/2))_(n)Si(E)_((3-q))R¹ _(q), wherein each R¹ is independently a C₁ to C₃₀ hydrocarbyl, n is 10 to 400, q is 0, 1, or 2, E is a hydrolyzable group containing at least one carbon atom, and b) an organosiloxane resin comprising at least 60 mol % of [R²SiO_(3/2)] siloxy units in its formula, where each R² is independently a C₁ to C₂₀ hydrocarbyl; in c) an organic solvent; to form a resin-linear organosiloxane block copolymer; wherein the amounts of a) and b) used in step I are selected to provide the resin-linear organosiloxane block copolymer with 40 to 90 mole % of disiloxy units [R¹ ₂SiO_(2/2)] and 10 to 60 mole % of trisiloxy units [R²SiO_(3/2)], and wherein at least 95 weight percent of the linear organosiloxane added in step I is incorporated into the resin-linear organosiloxane block copolymer; II) reacting the resin-linear organosiloxane block copolymer from step I) to crosslink the trisiloxy units of the resin-linear organosiloxane block copolymer sufficiently to increase the average molecular weight (M_(w)) of the resin-linear organosiloxane block copolymer by at least 50%; III) contacting the resin-linear organosiloxane block copolymer from step II) with a stabilizer, wherein the stabilizer comprises alkaline earth metal salt, a metal chelate, a boron compound, a silicon-containing small-molecule or combinations thereof; and IV) optionally, removing the organic solvent. 19.-27. (canceled)
 28. A method of increasing the trouser tear strength of a solid curable film composition of a resin linear organopolysiloxane comprising adding to the composition a stabilizer comprising an alkaline earth metal salt, a metal chelate, a boron compound, a silicon-containing small molecule or combinations thereof.
 29. The method of claim 28, wherein the trouser tear strength is at least 0.5 kN/m.
 30. The method of claim 29, wherein the boron compound comprises a a boronic acid.
 31. (canceled)
 32. The process of claim 30, wherein the boronic acid comprises phenyl boronic acid.
 33. The method of claim 28, wherein the trouser tear strength of the solid curable film composition is increased by at least 20% with the addition of the stabilizer, relative to solid curable film compositions lacking a stabilizer. 